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Character:

Reborn`s "partner" is a shape-shifting chameleon named Leon, who usually sits on Reborn's fedora. The bullets used by Reborn are created inside Leon. When Reborn's student is gradually progressing, Leon's tail falls off, his shape-shifting abilities become unstable, and he is no longer able to create bullets. When Leon shape-shifts into a gun, a move Reborn uses is called Chaos Shot, which is a shot that branches off with the sun dying will flame.After Leon creates special items for the student, he returns to normal.

Source from Wikipeida