Clothes and hairstyles. Is really difficult in a Honey Select game to make 6 differents girls, 3 of them being related and being capable of make different hairstyles without making the girls look like clones. Only Penny and Nancy look alike in some frames, but the poses and attitude helps to difference them, and the easy solution is just make a hairstyle for every one of them but no, Caribdis plays with everyone of them in everyone of the updates. It's funny to me that the ones with unique characteristics, Nova with the patch and Luna with the red eyes are the only ones that don't really need them.
Top tier character designs, I envy him a lot for that, is raw talent surrounded by hardwork, and every update is better and better on that.