Oh, I didn't expect a Japanese AVN but I think I can work with that, thanks!
A short dip into AVN design: The problem with personality-rich MCs is that if the player can't vibe with him, they'll likely drop the AVN right away. So a fraction of potential players is instantly gone just because of that. That's why devs usually opt to make a plain, self-insert-friendly MC and put the spotlight on the NPCs instead. If you don't like a girl's personality you can usually avoid her, but that's not possible with the MC.