The Sealed Sinner’s Prison (罪人の封牢 Zainin no huurou) is a location in Monster Girl Quest. Situated in the east of Hellgondo, it was created by Goddess Ilias as a prison for those who rebelled against her.
Due to the way it contains its prisoners, the Sealed Sinner's Prison does not look like a traditional prison. It instead consists of a simple monument with a central altar where the name of its captive, Heinrich, is inscribed. The prison keeps its captive restrained through holy energy, which seems quite strong as Heinrich is still sealed within despite the building being in ruins.
Ilias created the prison to serve as the ultimate punishment for rebels. It seals them for all eternity, preventing them from reincarnating.
The prison is first mentioned when Luka and Alice arrive at San Ilia castle. When Luka talks about Ilias’s third commandment, Alice mentions a rumor about human souls being sealed when they break her commandments.
When Luka and Alice arrive in Hellgondo, Alice explains the purpose of the prison. Luka feels that something in there is calling out to him.
Upon entering the prison, Sylph is unexpectedly in a good mood as the place smells like her former master. They then notice the inscription on the monument: Heinrich Hein. This leaves them to wonder what truly happened to him, as according to legend, Ilias brought him to heaven. Their only conclusion was that he rebelled against her. Luka is in complete disbelief, but Alice tells him that standing around won’t bring any answers. As they leave, the Angel Halo suddenly shines with light then fades, seemingly reacting to some form of presence in the prison.
After Ilias declares war on humanity and Alice's followers, Tamamo finds out through Promestein's discs that she there is a worldwide seal deployed on the Four Towers that weakens the Four Spirits, preventing Luka from unleashing his full power. She then devises a plan such that they can replace that seal on the spirits with a seal that weakens the holy energy of the angels, making them vulnerable. She tasks Luka and Alice to copy the data of the holy seal on Heinrich in the Sealed Sinner's Prison.
As the two protagonists arrive there, Black Alice appears, intending to toy with Luka while Alice copies the data. After a brief battle, Chamaeru, Granaeru, Runaeru, and several Veteran Angel Soldiers appear, having been sent by Seraph Eden to deal with Luka. The angels accuse Black Alice of interfering with Ilias's plan, prompting the 8th Monster Lord to leave. Suddenly, Heinrich's soul appears and possesses Luka's body, possibly released by Alice's interference with the seal. Heinrich swiftly defeats the angels one-by-one, demonstrating his own techniques: Quad Spirit Summon, Element Spica, and Quadruple Giga. However, once all the angels are dealt with, Heinrich's soul has worn himself out and fades away. Alice reminds Luka of their objective and that she has completed it, and the duo make haste back to the Monster Lord's Castle.
The Sealed Sinner's Prison didn't exist 500 years ago during Black Alice's ruling days in Monster Girl Quest Paradox.