Left

Left is the black part on the left (the character's left). He's part of a specie of beings either white or black that are soulmates with another member of the specie of the opposite color. They can fuse together to become stronger !

However, a character named Dante came to their world to destroy it, and most of them are dead. To save his soulmate, Right, Left fused with her as she was about to die. She's in a permanent coma phase while being fused with Left, and that is the only thing keeping her alive. Left is trying his hardest to find a way to save her .