Buso Renkin

Before Dr. Butterfly dies, he explains that a man named Victor is inside the flask and that he is a being far superior to humans and Homunculi. Kazuki destroys the flask and engages Victor in battle and is seemingly killed after having his kakugane destroyed. Kazuki regains his kakugane which is revealed to be a black kakugane, causing him to transform into a being like Victor with glowing light green hair, red eyes, and tanned skin.