Game Master and Satan Slave

 is the tenth episode of the Trinity Seven series, broadcasted on December 9, 2014 on  Fuji TV.

Synopsis
The ultimate demon lord, Astral Trinity, shows up in the form of Arata with a grotesque new appearance. Hijiri appears as well, and the others discover that she is a high-level mage whose goal is to kill Arata and destroy the school.

Summary
As Astral Trinity appears, he forcibly dispells Ilias Fragment's magic, revealing her true appearance while also liberating Sora from her imprisonment. However, in a display of power, the Demon Lord also summons a Breakdown Phenomenon which begins destroying the surrounding area. The situation then prompts a recovered Mira and Sora to confront Astral, but are easily defeated due to his anti-magic. Subsequently, the demon senses potential in Trinity Seven, demanding she submit to him before attempting a kiss, causing Mira to slap him in protest in favor of Arata. Fortunately, her action manages to disrupt Astral for an opportunity for Sora to seal the Lord and return Arata to his normal state. Although Arata has returned, the group remains confined within the consealed barrier, controlled by Ilia whom would have to be eliminated. Instead the Demon Lord Candidate requests that she join him in the real world, grateful for her support as Hijiri despite the grimoire's earlier actions. However, due to Astral Trinity's Breakdown Phenomenon, she has lost control of the reality which forces the team to combine their magic in order to destroy the magic anomaly.

With Ilia's support, their plan is successful, returning them to the original reality before reuniting with Lilith and Akio. As the group decides to recover in a safe location, a mysterious group including Hijiri observes the party before the missing cousin notes that Arata and she have become enemies.

After locating shelter, the girls discuss Arata's transformation into Astral, prompting Akio to suggest his elimination due to the dangerous nature he possesses. However, the Trinity Seven quickly dismiss the idea before changing the subject to their suspect behind the incidents, Hijiri, whose true identity as a powerful magus and connection with the Demon Lord Candidate is concerning.

Later, Hijrii approaches Arata and the two are happily reunited, but their circumstances has forced them to become enemies. As such, she attempts to eliminate him until Lilith intervenes, although the Trinity Seven's ambush is ineffective. The teacher shortly deduces that Hijiri also possesses a Demon Lord Element which the cousin confirms, acquiring the candidacy following her disappearance. Thereafter, Hijiri next transforms into her Demon form, Satan, revealing that she also mastered the Trinity which causes Lilith to immediately protect Arata from the Candidate's upcoming spell. However, the unexpected appearance of Arin, summoned by Arata while possessing the Demon Spear Gae Bulg, is able to neutralize Hijiri's magic before Akio and Mira soon arrives. As a result, the Demon Lord Candidate decides retreat while noting that her companions, Iscariot, will be able to easily destroy the Royal Biblia Academy due to the lack of Trinity Seven members. Following her withdrawal, the party decides to quickly return to the Academy in order to support Levi and Yui while Arata resolves to reach his cousin again.

Meanwhile, an unknown girl observes the destruction of the Royal Bilbia Academy from above.

Characters

 * Astral Trinity
 * Arata Kasuga
 * Ilia
 * Sora
 * Mira Yamana
 * Lilith Asami
 * Akio Fudo
 * Hijiri Kasuga
 * Arin Kannazuki

Cameo

 * Lugh
 * Master Liber

Adaptation

 * 24. Game Master & Exodus
 * 25. Luminas & Satan's Rage


 * 26. Fianna Knights & Invidia Magus

Alterations

 * Ilia originally attempted to release the barrier before discovering that she had lost control to Astral Trinity's Breakdown Phenomenon.
 * Lilith's intervention during Arata's reunion with Hijiri did not originally occur during the latter's incantation.