All in all I think this game has a lot of potential. The storyline is engaging and the characters interesting and likeable.
Some recommendations I have.
During the Evie sex scene, perhaps lengthen her orgasm. Currently it lasts about 1 second I would recommend making it 3-5 seconds so the player doesn't have to keep rolling back the scene to appreciate the orgasm.
Making the erotic scenes repeatable could potentially be a good source of affection for the character. However to prevent players from just farming the scenes to max out the character levels, perhaps add a cooldown to the erotic scenes.
I can't help but notice that you are using Koikatsu style characters. If you are then it would be cool if later in the game, side characters appear as the town seems to be on an upswing. These side characters could be farmers, townspeople, other miners, generally just people to populate the background in the various locations. From there you could interact with these characters and have generic erotic scenes with them.
Going back to the Koikatsu style of characters, one of the features in Koikatsu is allowing the player to "edit" their classroom to their hearts desire. Should you implement side characters then having an option to use your own characters rather than the default characters would be fantastic.
That's all I have, I'll certainly be keeping an eye on this game in any future releases. Keep up the good work
Komisari