Kurasu marugoto jingai tensei -Saijyaku no sukeruton ni natta ore- (Associated Names)

When I opened my eyes, I somehow was in a monster house! The class idol became a slime! That quiet librarian girl became a succubus! And I became a skeleton…Everyone reincarnated into strong and awesome monsters, yet I am a useless protagonist. This is the story of how he who became a weak skeleton will…