Oboreta Saki no Ori no Naka

The man who appears before Koki is Ryo,
who says he wants to make Koki into his pet.
In desperation, Koki agrees and begins his life as a pet.
Just as he is getting used to this life, his former best friend Asakura appears.
Asakura wants to return Koki to his former life, but Koki may be too far gone...

[From DLsite English]