I read the whole manga, and i am still disappointed at the shitty ending it had for Kirio, (on top of the actual ending with the harem pull, and final boss being frankly quite normal looking), however apparently in the anime directors-cut they went the extra mile to shit on Kirio and made him instead of a kidnapped kid that was experimented on, they made him the end result of the excrement of the nine-tales in the shape of a boy.

So not only is he repeatedly shit on just because he is a guy in what is essentially an action harem story, now! he has to pass from the symbolic to the literal sense of being shit on!

Really nothing goods happens to him, he ends homeless and is "adopted" out of pity, just for Inoue to then hardly even remember his name because she is so obsessed with Tora, for everyone he is like some scribble in some wall, for real he was better living homeless with Kuin and forgotten by the author, i see no need to bring back a character just to shit on him.