Rei is a character in the Devil Children series.
Devil Children White BookEdit
He is a Phoenix and the demon partner of Takaharu Ougi. Haughty and arrogant, Rei blindly follows the angels and their goals. He tends to goad Takaharu into believing in their more dubious actions being for the greater good andlooks down upon demons and Devil Child's, which results in him getting into fights with Clay and starting fights with him. He is later shocked when he learns that the angels goals weren't as noble as he believed.
Like Takaharu he is fused with Starhair near the end of the game to empower her. Rei is released from her after Jashin's defeat. After beating the game he can be swapped with Clay and act as Masaki Kuzuha's devil partner.