Narumi Asai

Narumi Asai/Seiji Asou was not a recurring character, only appearing in one arc, the Moonlight Sonata arc. He was a man, but by changing the pronunciation of his name, he was able to live as a woman. He did so to get revenge on the men who murdered his entire family, he himself only escaping because he was not on the island at the time, instead being in a hospital on the mainland. He killed those who were respnsible for the fire that killed his family, then killed himself. (He regrets the murders after realizing the message from his father: live an honest life) Despite this, he has remained popular in some parts of the fandom. This was only exacerbated by Conan's statement ten volumes later that he was his greatest failure