|First Appearance||Devil Children Black Book|
|Demon Partner||Cool the Cerberus|
|Japanese VA||Shōtarō Morikubo|
- Devil Children Black Book & Red Book
- Devil Children White Book
- DemiKids Light Version / Dark Version
- Devil Children Fire/Ice Book
- Devil Children Mobile
- Shin Megami Tensei: DeviChil
Devil Children Black BookEdit
Setsuna Kai has a younger half-brother named Nagahisa Kai, who was kidnapped and taken to the Expanse. He enters the demon world along with his demon companion Cool to rescue his brother. During the course of the game, Setsuna discovers he is a DemiKId - half-human and half-demon - and that he is the son of Lucifer. He learns this from the ghost of his mother and Mammon. He also learns Nagahisa is an Angel Child and the son of Michael, and that he was kidnapped by demons to prevent the angels from finding him and abusing his power. The two of them have the power to either bring peace to the human and demon worlds, as Lucifer wishes, or to destroy and purify them in cleansing flames, as Michael and the other angels wish. Should he choose to face his brother, Setsuna will end up killing him. Then he will have the choice of either recreating the world or becoming the new God of the Stars when he meets Hoshigami.
Devil Children White BookEdit
Setsuna lives in the same apartment as his half sister Mirai Kaname and the two are dragged into Masaki Kuzuha's quest when demons attack them by mistake. He can swap demon partners with Masaki in the epilogue.
DemiKids Light & DarkEdit
Serina is a S-Rank BattleNet opponent. Cool and decisive in battle; he desires to be the best in the BattleNet. After giving the protagonist the second demon, he will tap into his latent demonic power as an inverted star appears on his forehead, with his hair becoming spiky and pointed. He gives a Nex after 15 defeats, Meta Nex after 25, Neo Nex after 30, and King Nex after 40.