OMFG, no .... no..... nooooo GOOD fathers do NOT F their D. He is absolutely grooming her by all classic definitions of the term. So what, there are tons of horrible character traits in these games. This game just happens to have this fetish as part of its theme.
First of all, it didn't even start like "Hey, I get to see my daughter after so many years, I'm gonna fuck her!".
Secondly, even when the MC came to terms that he loves D more than a father loves his daughter, that he loves her more than as his daughter, he's still been very much a father to her, more father than a "boyfriend", sure his incentives have changed quite a bit, but don't they always when you're first close to someone on a platonic level and suddenly you develop romantic feelings for the person? And if you say no, then you've never been in love, the incentives ALWAYS changes when you fall in love with a person, and in MC's case he now has double the reason to be the best he can be for his daughter, as a father and as a lover. And even now, he's still being careful with her, he doesn't want to cross any lines that he thinks she may not be comfortable with or willing to, he's not pressuring her at all and if she would decide not to engage in penetrative sex EVER, he'd be fine with that, he's fine with whatever she wants, so no, he's not grooming and in fact he has given all the control to HER, she decides where things will or will not go, not him, he's not even giving her any ideas, it's actually Elena that has directly or indirectly given her ideas. And MC giving her oral and so on actually came to be because she always failed in her own attempts to let off some steam, it's not like the MC one was "Well, now we've got the kissing part of the couples training done, now lets do this to further your training".
