Arata Kasuga (春日 アラタ, Kasuga Arata) is the Demon Lord of the Superbia Archive and main protagonist of the series, possessing the ability to nullify and copy magic. After a Breakdown Phenomenon destroys his hometown and causes his cousin Hijiri Kasuga to disappear, Arata becomes determined to save her by becoming a Magus and transferring to the Royal Bibilia Academy where he fatefully meets the Trinity Seven.
Arata has a carefree and cheerful personality who is usually bantering and teasing others even in dangerous situations. He is also noted to be very perverted, often finding himself in risque situations or confessing his desires towards a girl. Usually, this is by complete accident, but he simply rolls with it and lets himself enjoy the situation without getting worked up about it. During these situations, he usually quotes: "Thank you for the treat" or something to that effect. This often earns him a scolding from Lilith Asami and scorn from Mira Yamana, the Top Seat of Grimoire Security, who calls him filthy or impure. Other girls such as Levi Kazama, Akio Fudo or Lieselotte Sherlock don't particularly mind and often goes along with his remarks. However, he knows where to draw the line, as he refuses a kiss from Yui Kurata because that is only for "when we're closer". In times of need, Arata can become very dependable. He is very calm under pressure, in both perverted and dangerous situations. His natural way of thinking allows him to make rational decisions and develop solutions to problems that would cause others to panic. Arata cares very deeply for others, especially his friends. He is willing to risk his life and become stronger to save those he cares about, such as Lillith, Yui, Lieselotte, etc.
Despite his perversion, Arata has a mature view of relationships. For instance, he refused a kiss from Yui due to believing that was something they should do when they're closer. Furthermore, as seen in the Ova, Arata will not take advantage of girls who are vulnerable to physical needs, showing he has some respect for women.
There are two known instances that can cause Arata to lose his cool. The first is Hijiri Kasuga, who is his entire motivation for becoming a magician and his driving force for most of the story. Lieselotte was able to shake him mentally by offering information on her whereabouts, and when the two of them finally do meet he single-mindedly tries to take her back. The other is someone disappearing due to his own powerlessness, a trauma developed by Hijiri's apparent "death". The first time this happens, he triggers Astral Trinity's awakening to prevent it.
During the Sky Library Arc, Arata admits that the Trinity Seven members are essentially as important to him as Hijiri is, showcased by one of his very rare shows of anger towards Abyss Trinity for hurting Akio.
Following his transformation into a Sword Magus, he has displayed signs of aggressiveness occasionally, catching the notice of both Akio and Selina Sherlock.
- Main article: Astral Trinity#Personality
During moments of emotional stress, Arata's behavior greatly changes after transforming into Astral Trinity, becoming quite cold and ruthless in contrast to his normal behavior.
Arata is a slender young man, with shaggy cut dark hair, and dark eyes.
Initially, Arata usually wore his first high school uniform, the top half consisting of a black t-shirt, worn over by a white dress shirt and an unbuttoned black gakuran jacket. The bottom half was simple black pants and penny loafers.
When he transferred to the Biblia Magic Academy, he mainly started wearing the Academy's uniform, which also consisted of a white dress shirt, black t-shirt underneath, penny loafers, dark suit jacket with the school symbol on the breast pocket, and pants. However, he now includes a vest over the dress shirt and a red tie. Normally, he wears the dress shirt top button unbuttoned and untucked with the tie loosened. In casual attire, he wears a looser variation of his school attire. Arata also usually wears his grimoires in the fashion of a necklace or tied around his hand.
Currently, Arata received the mark of the Magic King on his right hand after obtaining Judecca and learning three different archives despite not fully mastering Acedia.
After being reincarnated, using Ana's magic. Arata is now a size of a child, with the same clothes but now fitting his small size. Instead he wears a white t-shirt, and a black pants and penny loafers.
Originally, Arata wore a black mandarin collared shirt, a jacket with ruffled sleeves, dark pants and shoes, with a white sarong.
After copying Akio's Mantra Enchantment magic, his Magus mode changed to a white mandarin collared sleeveless shirt, worn over by a black sleeveless stand up collared jacket. The bottom half consists of white pants wrapped around by a strong and tied with an abrasive belt. As a small child, reincarnated by Ana's magic, his Magus mode clothes hasn't changed, save now they fit his child-like state.
Trinity Form: Signifying that he has become a true magic king, Arata's attire in this form includes a white long-sleeved shirt, under a shoulder cape and collared vest with arm gloves. He also wears again white pants with knee-length boots, wrapped around with a waist-cloth, strong and belt. The shoulder cape, vest, sarong, waist-cloth, booths, and arm gloves have a black with white edges or cuffs design.
Upon temporarily attaining the level of a Paladin, Arata adorns a set of dark crimson armor consisting of a chest plate, gauntlets, tassets and thigh boots, worn under a dark tunic and pants, as well as a high collar cloak.
During his training with Arsha, Arata grew his hair longer which he ties into a ponytail with a hairband. Furthermore, his attire was overhauled to include a tunic worn under a short-sleeved jacket that covers his chest and fastened by a large belt, as well as metal gauntlets. The lower portion consists of a white cargo pant, sarong, and dark boots.
While invoking his magic to control a Breakdown Phenomenon, both his hair and eyes will begin to turn white, resembling Astral Trinity.
- Main article: Astral Trinity#Appearance
Upon transformation, Astral Trinity possesses Arata's body while retaining his main physical features with several alterations.
Born into a normal family despite being a Demon Lord Candidate, Arata lived an ordinary life until the death of his parents due to a plane crash of unknown cause at a young age. As a result, he would live together with his cousin Hijiri and her family. During elementary school, the two would develop a close bond with each other as Arata was the only one who treated her kindly despite not knowing she was a Magus.
In middle school, Arata would develop his perverted side, often encountering various embarrassing situations with Hijiri. As such, he was often chased by her every time, although this would also develop his resilience as well.
While his magic as Demon Lord Candidate awakened, one day after high school, Arata and Hijiri, secretly Sora (The Astil Codex) in disguise, were heading home until they passed under a highway. Suddenly, Arata's magic became wild, losing conscious while draining Ilia's magic and reverting to her original form. After regaining his senses, he became aware of the Black Sun and destruction surrounding him as the real Hijiri found him. He would become even more confused when Hijiri handed him a grimoire (Sora) and asked her to grant his wish. Afterward, she would leave him some last instructions before kissing him, asking him to remember her. To Arata's horror, he would then witness his cousin disappear in front of his eyes, unable to reach her before finding himself in an empty world. Bewildered and desperate to find Hijiri, Arata would demand the grimoire to return his normal days.
Stark Naked Magic
Arata's Thema is Imperium or "Rule" from the Superbia Archive, meaning that his magic is used to dominate and "rule" other. Arata's first and primary magic is nicknamed Stark Naked Magic, momentarily controlling all magic in the surrounding area and forcibly dispelling the magic. The usual effect causes an individual's Magus Mode to forcibly removed, often resulting in the victim's clothes being removed. As such, Arata possesses the strongest form of magic negations, capable of even dispersing many Breakdown Phenomenons. However, unless his magic is stronger, he cannot negate the magic of those stronger than him. Recently, he has learned to adjust the level to avoid stripping every piece of clothes. As a Demon Lord Candidate, as well as possessing both the Astil Manuscript and Ilias Fragment, Arata is capable of utilizing several unique abilities, notably the capacity to copy only the Trinity Seven's magic, regardless of the Archive or Thema. This feat is accomplished by his grimoires rearranging the magic into one he can wield through the following steps:
- Concept : Grasping the basic concept of the magic or Thema. Arata must confirm both the name and execution with his own eyes and ears.
- Understanding : Understanding the foundations, the "genealogical tree" of the magic by learning the name of the magic's founder from a currently using Magus.
- Reasoning : Analyzing the magic's fundamentals and disassembling its chemical structure, which simply means dismantling the magic's "nature" through the use of logic. This is done through Arata's stripping magic.
Upon completion, Arata then is able to access and cast spells with his own variation. Currently, he has copied three different users' magic:
- Outer Alchemic: The first magic he copied was Lilith's Abies Thema or "Outer Alchemic" from the Luxuria Archive, allowing him to use alchemy to form guns and firearms as she does. He uses this to direct his Anti-Magic abilities rather than throwing them randomly at everything in his vicinity. Using this directed version of his magic, he defeated a D-type demon dragon and dispersed his second Breakdown Phenomenon.
- Mantra Enchantment : The second magic Arata learned was Akio's Fides Thema or "Mantra Enchantment" from the Gula Archive, which gifts him the ability to enhance his body for defensive or offensive use, namely he manifests a dragon-like entity based on the D-type demon he had defeated before. Using this magic requires him to have a very strong determination.
- Logos Art : The third magic Arata completes was Liese's Stagna Thema or "Logos Arts" from the Acedia Archive, which grants him the ability to manipulate time. He is able to transport himself small distances and momentarily freeze time for a moment. Currently, he has not fully mastered Logos Arts, which has caused his magic to become unstable.
After Arin confessed her love which liberated from his imprisonment in the Library of Demise, Arata received his fourth Thema, Ruina from the Ira Archive.
Arata fulfillment of the Trinity (mastering three Themas) grants him the ability to use the Magic King weapon, the Black Imperial Sword Judecca. Along with his Imperium Thema of the Superbia Archive, he became an authentic Demon lord, gaining the Trinity Form and even performing Paladin level techniques. Additionally, he is able to see Spirits as one of the few people chosen by the world. However, this has resulted in his Demon Lord Element to drain him, causing pain and hallucination. As Arata continues to use his magic, he is slowly closer to becoming Astral Trinity. However, he has gradually been able to partially control the changes.
When Arata's magic goes out of control, he forms a very powerful Breakdown Phenomenon. A black sun appears in the sky above and proceeds to reduce everything below into base particles which it then absorbs, effectively wiping out a city in the first incident of its manifestation. Furthermore, a pair of black particles that take shape as wings will appear on his back.
Possessing great magical power as a Demon Lord, Arata may potentially already be immortal.
Notably, despite being a Demon Lord Candidate, Arata was born as an average child with no magical abilities to a normal family until he awakens his magic in high school. 
Upon transferring his magic to Anastasia-L in order to stabilize her existence, Arata forfeited his Demon Lord Element which rendered him a normal mage. Although Arata initially had difficulty controlling his magic, he has since managed to regain control, as well as gaining a large amount of magic capable of confronting the Twelve Demon Commanders after partially merging with Judecca. However, he later gained the Demon Lord Element by becoming a True Demon Lord like Deus Trinity.
Much Later Anastasia-L transferred her reincarnation magic to him which allowed him relieve a new life. This magic is extremely useful as it helps someone escape death. This magic activates automatically upon Anastasia-L process of disappearance. Since it's Anastasia-L own life, the reincarnated will reincarnate in their own life style. This is probably the reason why Arata reincarnated as a child.
Upon retrieving his magic which has been stored within Hermes Apocrypha, Arata temporarily attains the level of a Paladin, allowing him to use more powerful spells of Outer Alchemic as well as becoming capable of defeating homunculi.
Sword MagusAfter forfeiting his Demon Lord Element, Arata trained with Anastasia-L and Arsha to switch his class into a Sword Magus, regaining the capability to wield Judecca while also granting him the ability to load his Thema into the Demon Lord Weapon.
Additionally, the level of his magic is also significantly increased, such that if angered, he is capable of dominating the magic around him.
However, upon exhausting a majority of his magic, Arata is unable to maintain his fusion with Judecca which requires him to rest until he recovers.
Furthermore, Arata has become adept in combat tactics, capable of providing guidance and directions to his friends during battle.
- Meteo Punisher - Using a gun, Arata can shoot a large blast of anti-magic towards a directed path. This attack is capable of erasing a Breakdown Phenomenon.
- Meteor Dragonar - Activating the Outer Alchemic spell Realize and Mantra Enchantment spell Conception at the same time, Arata creates rifles and shoots a large burst of anti-magic in the form of a dragon. This attack is capable of dispersing a Breakdown Phenomenon. Furthermore, the spell can be utilized by another mage by transferring his magic.
- Impel Majester - Arata's stripping magic, that he uses to disassemble a persons magus mode and thereby clearing the third process of copying a person's magic.
- Domination Territory - Arata touches the said person, and enter their inner consciousness, which he has absolute control over the space.
- Realize - Activating a macro in the Astil Manuscript, Arata can use Outer Alchemic to create a weapon such as a handgun or a rifle.
- Conception - Taught to him by Akio, Arata uses his determination to create a single magic character on any part of his body, usually on his fists, chest or forehead. This spell will strengthen the body part the magic character is on, giving him defense against most physical attacks. Furthermore, he manifests and freely controls a dragon-like entity, based on the D-type demon during Yui's Breakdown Phenomenon. This dragon is capable of nullifying any magic.
- Chrono Calculation - This spell allows him to teleport short distances.
Demon Lord Weapon
- Main article: Black Imperial Sword Judecca: Techniques
- Baal Reincarnate - A time leap macro on the same magic level of the Last Crest. Arata, with the help of Lieselotte, controls the magic and reverses an opponent's magic.
- Realize: Buster Mode - While in Paladin mode along with Lilith's support, Arata summons and controls a laser sentry gun.
- Meteor Buster - Fires an alchemic laser blast from a sentry gun capable of significantly damaging a Demon Lord.
- Main article: Astral Trinity#Abilities
Due to his nature as a Candidate, Arata can transform into Demon Lord Astral Trinity under stressful situations. Under the influence of Astral, Arata's magic and strength are augmented enough to overwhelm grimoires and the Trinity Seven. Arata himself is also aware of the Demon Lord's actions during the possession. However, if someone is able to distract Astral for a moment, his grimoires can revert his state and return control to Arata.
In the Beta universe of Liese Chronicle side story, after β-Liese is defeated, the Demon Lord Element she stole is returned to Arata. Along with that, the essence of Logos Art she learned also got absorbed, changing Arata into Acedia's Blue Demon Lord - Chrono Trinity.
As Demon Lord of the Acedia thema, Arata is able to draw the Demon Lord Weapon - Blue Emperor Sword Antenora (from the name of the second ring of 9th hell in Divine Comedy) from the universe with the possibility to get that weapon.
He can also create dimension, which when crashed to another dimension, will cause mutual destruction.
- Astil Manuscript - A legendary grimoire that once belonged to Hijiri, the Astil Manuscript has since contracted with Arata once he became a Magus. Said to contain "information from another world", the grimoire is able to perform numerous magic, giving Arata a great deal of abilities. Originally, she was capable of granting Arata's wishes of returning to his normal days by restoring his destroyed hometown and inhabitants in an alternate dimension. After undertaking with him, Arata received the ability to copy other people's magic, under the right conditions, even from different Archives and Themas. This is possible through the Astil Manuscript modifying the magic in a way that Arata can use it. Furthermore, having its own will, the Manuscript can also take on multiple forms, transforming into Hijiri or her true appearance, Sora. As Sora, she is able to act independently from Arata, performing her own magic which allows her to support Arata externally. When he becomes Astral Trinity, she was able to revert him back to normal. After Arata forfeited his magic, Sora can only materialize her human form, but nevertheless, considers him to be her master.
- Ilias Fragment - Another legendary grimoire, the Ilias Fragment also originally belonged to Hijiri before joining Arata. Like the Astil Manuscript, she shares many numerous abilities such as transformation, world construction, magic analysis, etc. She was also capable of controlling a group specters and even managed to trap Sora. Described as a "support type grimoire", she mainly assists Arata through increasing his offensive power, stabilizing his magic and healing any wounds. Like Sora, she is able to transform into different forms such as Hijiri, who she often took her place when Hijiri had to leave to magic business or her true appearance as Illya. In her human form, Illya is also able to act separately and support Arata with her magic externally as well. In spite of Arata's loss of magic, Ilias nevertheless continues to remain loyal to him as his grimoire.
- Black Imperial Sword Judecca - A Demon Lord Weapon originally sealed away in the Sky Library to be used against the Demon Lord, Arata would ironically release the sword and become its master. Possessing a will of her own, usage of Judecca required the user to have the Trinity, which Arata initially failed and almost forcefully reverted back to Astral Trinity again. Eventually, he would surpass the requirements by mastering four Archives and become the owner of the weapon. With his acquisition of Judecaa, Arata's magic increases tremendously, allowing him to fight on par with powerful opponents. The sword also allows him to use multiple magics from those he copied at the same time to perform even Paladin level techniques. Furthermore, Judecca is also capable of destroying a single Breakdown Phenomenon. Judecca is also capable of changing its appearance, shrinking into a smaller version of itself as well as a human form. Furthermore, he can also summon the Demon Lord at his choosing. After Arata relinquished his magic, Judecca temporarily cared under Abyss.
- Red Imperial Sword Caina - Allowed to borrow from Abyss temporarily, Arata would dual wield Caina and Judecca to simultaneously destroy a Superbia and Luxuria Breakdown Phenomenon.
- Arata's surname Kasuga means "spring" (春) (ka) and "sun, day" (日) (suka/suga).
- Out of the Trinity Seven, Levi Kazama is the only member that Arata has not been able to strip with his magic and he considers this to be the final frontier.
- Hijiri Kasuga, Levi, Yui Kurata and Lieselotte Sherlock have all at one point or more kissed Arata on one part of his body.
- Lieselotte holds the most records of three times for kissing him on the lips. Hijiri comes in second with one prior to disappearing.
- A running gag in the manga has, Arata always saying " Thank you for the feast " When he sees one of the Trinity Seven members naked.
- Despite being a Demon Lord Candidate, both of Arata's parents were normal people without magic. Although, the brother of Arata's father, Hijiri's father, including Hijri and her mother, were actually Magus'.
- Saitō, Kenji, writer. Art by Akinari Nao. Vol. 3 of Trinity Seven. Yen Press, 2015. Print.
- Kenji, Saitō, and Nao Akinari. "Principle & Break Zero." Trinity Seven: 7-Nin No Mahoutsukai The Novel - Night Episode to Memory. Yen, 2014. Print.
- [Saito, Kenji (w), and Akinari, Nao (i).] Trinity Seven, Vol. 7 (Nov 2016), Yen Press.
- Saito, Kenji, and Nao Akinari. 2017. “Impel Arm & Trinity Process”. Trinity Seven: The Seven Magicians, 8:80–118. New York, NY: Yen Press.