From his understanding, Lucien knows that if Kaneto only took Akane, and left him, his mother would've never told him about the torture she experienced. After all, she was like that, she never wanted Lucien to avenge her —she is fine with it, she once said.
However, this side of her hurt Lucien the most, because when it came to him, she was the first person to avenge him, even when she was powerless. Also, this is why, he felt pained by what Kaneto did to her: she fought for Lucy, but he didn't try to save her, when she was being tortured before him.
With how Akane assisted him on some issues, the anger Lucien felt from that day increased. Furthermore, when the kyuketsuki appeared, he was too powerless to save her, increasing his anger.
However, his anger is not that of hate, but that of love towards him and his mother. In addition to that, his anger carries a question:
"Why did you do it?
