Series: Silver Chaos (PC Yaoi Game)
Notes: Adonis is one of the characters in the very yaoi game Silver Chaos. My Japanese is still pretty poor, but the game is very easy to navigate and it is pretty self-explanatory - apparently, his friend/lover Maito (Might) was injured, and Adonis performed some dark spell to save him, and wound up being taken away by a demon. The game revolves around Maito going after Adonis to save him [and all of Maito's sexual escapades in the meantime ^_~].
Adonis shows up later in an evil (and sexy) form!