Gaap is the 33rd spirit of the Goetia. He is a great President and a mighty Prince. His office is to grant men knowledge of philosophy and all liberal sciences. He can cause love or hatred, make men insensible, and can teach you how to consecrate those things that belong to the dominion of Amaymon, his king, and can deliver familiars out of the custody of other magicians. Gaap can tell of all things past, present, and future and can transport men very quickly from one kingdom to another. He rules over 66 legions and was of the order of Power.
Gaap is the Angel sealed away by the Messiah using the Messiah Riser ages ago on Valhalla and is the final boss of Akira's route. In order to revive himself he resurrected the Imperium and used the Angels and Demons that make up the Imperium's army to collect the Four Crystals that will free him from his prison. His servant Scathach succeeds in forcing Akira to revive him. Upon his revival he rewards Scathach by devouring her soul. In the battle against him his resistances change due to the crystals around the area. When a crystal is attacked once he will teleport there and release a wave that pushes Akira and any demon away from it. He will no longer teleport over to the crystal if it's attacked again.