“Favorite supporting male anime character”
I thought about a few different characters, but wound up coming back to the first one I thought of.
Kurama, also known as Yoko Kurama and Shuichi Minamino, from Yu Yu Hakusho. (Yes, that is a guy.)
Another smart, strategic fighter, though unlike some characters of that type he never falls behind in power. Kurama’s control over plants is actually an amazingly versatile ability.
When the demon fox Yoko Kurama was wounded, he put his spirit into a human baby. He intended to remain in the human world for only as long as it took to regain his strength, but he came to care for his human mother, and went so far as to sacrifice his life to save hers, only to be saved by Yusuke’s own willingness to sacrifice his life. Somehow this worked out as none of them dying, and Kurama was obviously indebted to Yusuke after that.
Kurama strikes a rare balance; he suppresses his emotions in battle (unless someone is stupid enough to threaten his mother, in which case he brings out the tranquil fury) without ever giving the impression that he doesn’t have them, unlike a lot of other “logical” characters. And his silver-haired fox-man-demon form is pure badass.