Wait, is this the game I used to play back when it still using Koikatsu? The Keisuke's route first cutscene still look the same.
Koikatsu is not used and has never been used for any assets in this game, but some of the art is "borrowed" placeholder art in the process of being replaced. The game did just get a massive update to Keisuke's first CGs with new and replacement art, but that update is not public yet (but will be in about 2 months).