The Sealed Sinner’s Prison (罪人の封牢 Zainin no huurou) is a location on Hellgondo, found far in the east. It was created by Goddess Ilias and seals those who revolted against her as the ultimate punishment: to be unable to reincarnate and remain sealed for all eternity. Heinrich’s name is inscribed on the jail, which suggests that he went against Ilias and sealed his own fate (which is later revealed to be true).
Due to the way it contains its prisoners it does not look like a traditional prison, but as some sort of simple monument with a central altar where the name of it's captive 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.
The prison was foreshadowed 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 and is simply an area to fuel Luka’s curiosity, though he 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, who intends to toy with Luka while Alice copies the data. After a brief battle, Chamaeru, Granaeru, Runaeru, and several Veteran Angel Soldiers appear, whom were sent by Seraph Eden to deal with Luka, accusing Black Alice of interfering with Ilias's plan, prompting the 8th Monster Lord to leave. As Luka engages a stance, Heinrich's soul suddenly appears, possibly released by Alice's interference with the seal, who swiftly defeats the angels one-by-one using his own soul and Luka's body, along with 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.