It’s also ironic that his son/experiment was the one chosen by Mary’s technique in modulo to grant permission to end cursed energy as a concept. Like all the cursed energy Kenjaku ever needed came much later 68 years later by the same boy who he tried to dismiss (Yuta) and his accumulated cursed energy over the years and his offspring. He’d be so sick to his stomach if he’s seen what Yuji has done with his beloved cursed energy. But I suppose there’s a part of him that just might be proud he made something soooo resilient ? Yuji is the pinnacle of his experimentation he just never accounted he could make someone so good who was born from evil.