I see Issei as an incubus type of Devil, whose powers are powered by lust, and it just happens he loves boobs so that's how he can easily gain that lust. Of course it's assumed that between squeezing boobs and having sex, he'd pick sex. However, ecchi animes still have editorial limits.
The anime is kind of a mess when compared to LN... It's more of a collection of fan service, if they can put a way to show some boobs, they will. Even in serious situations, they will put fan service even for a few seconds, that's something that happens since the first episodes (Raynare randomly transforming and showing boobs), the LN is what I follow and prefer, and the series is taken much more seriously there.
That being said, humor is still present and that's something that will be within the game as well as I try to convey since the first seconds of the game. Of course there'll be serious moments too, but the love for breasts and humor is something I'll be keeping within reason.
There are some things I find too exagerated as well, like the power "
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"... Talking to breasts, it doesn't make much sense to me. I think it would make more sense for him to be fueled by lust (by any means) and speak to the soul of the woman instead. Almost identical, just a little more serious.
However, having those kind of powers in canon makes me feel more at ease to develop some custom ones of my own without feeling like I am going against the source material.
In R2 I've expanded the concept of "space" of Pailingual, while also implementing the paranormal concept of a Tulpa. It's a power that I believe fits his character, it allows me to put early hentai content, and it has also a purpose in the game (Being able to conjure them in battle).
So tldr, I think having a MC that loves breasts in a story with some humor is fine, but there has to be a balance and it shouldn't be too exagerated.
The main theme in this game will be building a harem, and growing stronger.
Of course this is still a hentai game, so the MC will be even dirtier, but it will be a build up.
Even if he enjoys breasts, he will do other things aside from squeezing them.