So... I like this game. A lot. There are some things here and there that I don't care for, but I can overlook them and enjoy the game for the most part.
What I can't overlook is how bad it feels to play through Naira's storyline. She's super sweet and incredibly trusting, affectionate AF - general waifu material. And I just hate how badly the MC treats her with no way to avoid it.
You sneak in and violate her privacy by reading her diary - okay, fine. That's common. But then rather than just knowing that info and enjoying it, you are forced to progress her story by stealing something super important from her, that you have zero knowledge of. Regardless of if you come clean about it or not, she forgives the MC without a second thought. Let me tell you - that is some grade A bullshit right there, and any normal human being would be right fucking livid rather than comparing it to stealing a pair of boxers... I would love to see an option introduced wherein rather than stealing it, maybe you leave it alone, and in a multi-part event, she wants to give it to you as a trial run because she wants to trust you, or to see what it's like. Or alternatively, maybe if you leave it alone it starts going berserk during a scene with her, and she /asks/ you to take it out of the box because there's so much mana she's suffering. Hell, as a third possibility, maybe if you leave it alone and just check up on it a few times, it starts to overcharge and you touch it 'cause weird stuff is happening. Just... anything besides the betrayal of trust would make so much more sense, and I think that every time I play.
Further, when she confesses her love to you and asks the MC to be her boyfriend - what the fuck? Why does he instantly agree to it with no dialogue options or serious repercussions? Being in a boyfriend/girlfriend relationship implies that it would be mutually exclusive. For all Naira knows, she's the only one you're fucking - meaning that by saying yes without any thought to it whatsoever, you're basically just cheating on her, a LOT. I feel like if you continue down her story like that, the only thing that's gonna come of it is heartbreak as she feels betrayed, and if she doesn't - well, I'd think that'd be in pretty poor taste even for a harem fantasy story. I'd enjoy it a lot more, or at least feel like less of a dick if you could tell her something like how you love her too, but you honestly don't feel like you could be held down to a single person in terms of your affections. Or tell her that if she wants to have that sort of relationship with you, that she should know you've been fucking the others, and that because you care for them as well, you can't just drop those relationships for her. Anything that would put the ball back in her court and let her know what's going on so she can make a decision about it would be a much better/more convincing relationship in my book. Fuck, maybe even establish at some point that nymphs are totally cool with having multiple wives to one guy or something so that she wouldn't find it odd or offputting. As it stands, she's reasonably and clearly jealous AF though as evidenced in the same event where she doesn't want to share you.
Also just as a side note, since you are progressing Iris's story a lot later than Fanora's developmentwise, I think it'd be fun to have a variant scene early on when Iris comes to get something from the stall where if you're already intimate with her, she instead of asking if you're Fanora's boyfriend and calling you losers has some sort of bashful or jealous reaction. I know that's tough with a semi-sandbox visual novel, but it'd be a nice touch.
TL : DR - I love this game. Please make the MC not a dick to Naira. (And if you haven't played the game yet, play the damn game. It's good.)