Demon King's Chess Piece

A mass of 'games' were held by the Witch's Senate in a competition on which would hold the most entertaining story. the protagonist was picked out for such a game by Featherine Aurora, and let loose into a fictional multiverse to bend to his will. He lost a lot of himself merging with a certain Demon King, but it can't be helped, he was given the option and took it! OCxHarem