BUCK is the best understanding of ZOE, but it took a considerable amount of time for them to get to know each other.
He was found in a fire in an old mansion in the middle of nowhere. The strange being was hidden from the public and was taken in by Macro Cosmos. However, he was violent and no one could stop him. Eventually they forced him upon ZOE, who had collected eight gym badges at the time.
BUCK has severe damage to his head drive, and is unable to make Silvally specific type changes. He also can't use Move, so he usually fights only with martial arts. Still, he is one of the strongest in the OTW.
Not many people know about his true past. He deceives his friends by saying that he was persecuted for his appearance. In other words, not much is known about him before the fire. However, to White Fang, who was mutually attracted to him, he confided his true past.

White Fang
https://www.furaffinity.net/view/40903255/