Shuu Iwamine is an interesting character because when the guy who he formed an intense one sided attraction to dies he has no problem with taking in the weird hybrid bird creatures he saved under his wing, but decided his flesh and blood son can get fucked
Ok but this is actually a really interesting question because I feel like his attitude towards Ryouta goes beyond misunderstanding or even animosity, he openly relishes in torturing him in ways that would make satan blush, and it's fascinating.
He not only interprets Ryouta's wish in the most psychopathic way possible, but also turns it into a tailor-made personal hell. He uses Hiyoko to be the first victim. It could have been any other human, but he goes for Ryouta's best friend.
"She was just there, it was probably out of convenience."
Ok, but then he scatters her remains around the school, including having Ryouta carry her severed head around in a box. Then sets him up to "kill" her AGAIN as Labor 9. Ensure with his own hands any remnant of her is destroyed. He methodically strips Ryouta of any way out, any hope, and any reason to turn back.
"It wasn't about Ryouta, he just thought it was funny."
Even as Ryouta comes to his senses, changes his mind and even graciously "pardons" Shuu despite all he has done, **Shuu still gleefully sends Nanaki after him to give him an impromptu vivisection**.
He doesn't treat any other character like this.
I'm not gonna pretend like I know why, but there are a few possibilities.
Maybe Ryouta reminded him of Ryuuji a bit too much in all the ways that don't matter, while at the same time failing completely to carry his essence. Too pragmatic and down to earth. Considerate and responsible. Plagued with mundane insecurities, putting his family and friends first. Average. He looks at Ryouta and Ryuuji is dead.
Miru and Kaku were not just Ryuuji's creations, they were Takaba lab's, their creations. Ryouta is from that Other Home Ryuuji had, the more important home by any social norm and logic, that he would go to when Isa was left all alone. Or that he wouldn't go to. Ryouta is a guilty conscience to Isa, who knows viscerally well how it feels to be neglected and always less important to a parent, but still silently relished in Ryuuji's presence. In the time that belonged to Ryouta that Ryuuji spent with him. A splinter. A reminder that maybe his beloved mentor was not as great of a guy in every aspect as he'd like to see him. Ryouta is an attack on Ryuuji's memory.
Treating Ryouta with no sympathy gives him emotional distance necessary not to confront any of this.
It's not like it matters he's Ryuuji's son. Ryuuji is dead, dead people don't care.
MERRY CHRISTMAS MERRY CHRISTMAS!!! [SHAD COOKED, SHAD COOKED!!!!]
