Once Larissa got Waveshot's confession, everyone finally understood what had happened.
Waveshot had been young when his home was raided and burned down. His mother had been with him, holding him even as flames took over everything. He didn't remember much from back then, only that the ghoul had been there and had confessed to his mother that he was the reason behind it all.
As such, the young man had left that day, thinking that the fire that had killed his mother had all been the work of the ghoul.
He hated the man, but he had believed him to have died, so there had been nothing he could do. As he aged, he also pulled himself away from the shadow of his father, making a good man out of himself.
However, when he had seen the man recently, all the past memories had flooded back, and he wanted revenge for what his mother had gone through.
