The back mystery with the red eyes villain and their attempt to resurrect the dead makes me wonder whether
Spoiler for speculations:
Yakumo could be a spirit resurrected into a body like that. It may explain how he got one red eye. Could be that any spirit resurrected into a living body contains one red eye?
And the villain then has control over that person? Would explain the convulsions we see Yakumo go through in the OP. It'll be interesting and sad if my speculation is true.