A few updates ago the mc was contemplating getting a room mate. I think each of the three main girls could benefit from this. Haruka could live in a spacious comfy apartment instead paying for a basic dorm room. Luna wouldn't be bothered by her brother and would have privacy when feeling frisky.
Violet would have a place to go if she definitely breaks up with her boyfriend. In case it's his apartment. They can save space if they sleep in the same bed.
Three people can fit in mc's bed comfortably as Haruka is slim, Luna is small and Violet is not much bigger than the mc. Hell, even all four if they move close together.
If they need more room for the girls' stuff they can move the computer desk into the spare room.
They could turn the free room into a proper play room by putting in a red heart shaped bed, painting the walls pink and decorate it with toys. Add studio lights and a camera setup.
Or if they feel especially adventurous, hang chains and pulleys with ropes from the ceiling and a some toys and tools on the walls. Change the old bed for one with a metal frame. Maybe put a st Andrew's cross on the wall for style. And paint the room black or dark red. If they have the money buy a gynecological examination chair. Imagine a sexy doctor Violet examining patient Luna.