I feel sorta bad for Toki, he never said he denies Towa, in fact in his thoughts he uses "She", not "He".
He's just pissed because with her out of the picture for owning the clinic, which no offense but, due to Japans overall attitude towards women, he basically is burdened with it.
Japans culture sorta forces him to think
"Well, I have to"
He is supposed to be the poster Japanese Son in his family, and he doesn't want a reminder that due to his own line of thinking(as I said, understandable due to Japans culture), he can't pursue his own dreams.
And just because Towa is accepted by her parents, she might not be the poster child of them. If she and Toki were both accepted mutually as equal, Toki wouldn't have this problem. However, he does have this problem, he is the Son his parents want to be for the sake of him feeling forced he has to be it.