Story
"Why am I forgotten from the whole world?" War between the five races on earth - the humans, the "Demonic Race", the "Wild God Race", the "Spirit Race" and the "Phantom Beast Race"- has ended in the victory of humans. It is said that "Prophet Sid" had sealed the other four races in the black pyramid now called "Crypts". Kai's job is to watch the crypts and make sure that there is no change. He is also training to save humans when the other races break the seal and come back to this world.
Synopsis via AniList (English).