Yoite is not a Mary Sue, there's nothing perfect about him, not even his power, and only Miharu and Yukimi actually bothered to know him beyond the "cold stone killer" facade or a weirdo that nearly everyone else think of him as.

THIS.

I don't care if you hate Yoite with a passion, just don't call him a Mary Sue because he is the farthest thing from that. And he is an important part of the plot/character development.