Hijiri Kasuga

Appearance
She bares a striking resemblance to Arin Kannazuki, though with more expression and presently longer hair. After being banished to the world outside, her hair has grown noticably longer and her left arm has turned black, although it's unknown whether the latter is due to the fact that she now uses a Magic King Element as a substitute for her body in the physical world, or other, as of yet unknown, reasons.

When she takes the form of Satan, her hair becomes even longer, she gains what looks like a crack on her face, her arms become black with claws, and her clothing becomes a dark robe-like dress.

Personality
In her first appearance, she has a tsundere-type personality. Obviously smitten with Arata, she nevertheless reacts violently (not without some justification, granted) to his perverted antics. She also becomes slightly distressed when Arata seems attracted to Azami Lilith, this however was actually the Astil Manuscript assuming her form and personality, implying this is how she was at home.

When the real Hijiri appears again, she is much calmer about Arata's antics, jokingly stating that Arata constantly did things like that, however, that's not to say it doesn't appear to bother her, rather, she's just gotten too used to it, to the point of being visibly awkward when talking about it. She exhibits Yandere tendencies, as she nearly kills Arata while claiming she'd just resurrect him later after she'd killed the Trinity Seven. She also shows small periods of extreme vulnerability to Arata, nearly collapsing in tears when he promises to take her back. She openly admits she looks forward to the day he can and will reach her, implying she's okay with failing her mission if it means she can be with him again.

Despite having been placed with Arata to monitor him, it appears she's genuinely fallen in love with him, to the point in fact that she's willing to fight the entire world itself for him. She actually managed to get angry at the world for using him as a means to its rebirth. Her true motivation is to destroy this system. She claims that she cannot forgive the world for taking away his ordinary days, proving beyond doubt that she values Arata more highly than the world, or anything else in it.

As stated above, she seems to be something of a Yandere. She can be somewhat intimidating, enough to make Lieselotte back down, but is ultimately prone to returning to her approachable demeanor when Arata shows up.

History
Sometime ago she was placed with Arata to monitor his development as a Magic King, while his parents were missing, claiming to be his cousin. She ended up fully integrating herself as his cousin, worse still, she ended up falling deeply in love with him, to the point of acting like a tsundere.

After Hijiri was engulfed by the "Breakdown Phenomenon" Arata created, she was expelled from the world to the "outside." It was truly a "world of nothingness," she learned how she'd been living in such a wonderful slumber, like everything until that point was a dream. But, somewhere inside, she was satisfied.

Then, as her sense of time was leaving her, and her consciousness was fading away. She was suddenly able to see into the "world" from the outside. There she saw a future, where Arata and the Trinity Seven had destroyed the entire world. The world had been reduced to nothing by the birth of the Magic King and the Trinity Seven. And then a new world was reborn. However, the Magic King and Trinity Seven would meet again, and once again the world crumbled. She watched the world be destroyed by the Magic King and the Trinity Seven over and over again. That was the future awaiting the world, a never-ending cycle with no way out. She knew the same would happen there eventually. A Magic King Candidate would become the Magic King, and together they would destroy the world. That was why she couldn't forgive the world for treating Arata as nothing but a tool for its reincarnation.

She didn't want Arata to become the Magic King of "Imperium," so she and Iscariot would destroy the world instead, and then make a world that Arata could enjoy freely.

Abilities
She has mastered Ruina, Baltan, and Analysis of the Ira Archive. By mastering three separate thema, she already has what it takes to be a "Trinity." She seems to cast spells using the magic system Chaotic Rune, which is based on Norse Runes.

Hijiri received the Magic King Element from the "Ruined World," after being disintegrated by Arata.

By making use of the Magic King Element and her Trinity status, she is able to take on the form of an archive. The manifested form of the archive Ira, "Satan". In this form, which exceeds Magus Mode, she is shown to be able to overwhelm the entire Trinity Seven at once.

Hijiri is powerful enough to simultaneously have contracts with more than one of the legendary grimoires, before even being a Magic King Candidate.

Hirji can't stay in the world for extended periods of time as her body has been broken down by Arata's Breakdown Phenomenon. At present she is nothing but an existence swaying between space and time. When she is not manifested into the world, she appears as a gemstone similar to the Magic King Elements, within which her body is visible.

Satan
Is the manifested form of the Ira Archive. In this form, Hijiri is capable of overwhelming the entire Trinity Seven at once. The transformation itself causes her visible pain however.

Baldr's Blessing
Baldr's Blessing is a Vegtam spell that encompasses both offense and defense. Baldr is also a legend among gods.

Arin Kannazuki
Arin and Hijiri have an unknown connection, as they are both not only physically identical, they use Chaotic Rune to work magic.

Trivia

 * Hijiri's manisfested form of Ira is a reference to the demon Satan. In Christian mythology, Satan is often considered the demon most associated with the sin of wrath. It can be assumed that this applies to other manifested Archives as well.
 * In the first print of chapter 0, Hijiri's hair color was initially brown in the color pages. However, in the volume 1, her hair color was changed to light blue which has been used since then.
 * It is currently unknown why Hijiri and Arin look almost identical to each other.