From what I'm experiencing so far... If you can't advance Rana or Klein's stories, you have to level them up more. I don't know what the threshold for each is, so I suppose you'd have to grind a bit, then wait a couple of days each time to see if they appear at Dorm 1F or elsewhere.
GOOD NEWS EDIT: So after you make the swimsuit, if you cannot advance to the beach scene, make sure you level up more (and possibly keep Adoi events to a minimum, though that's just my theory). After getting the beach scene, do some more leveling (40~45 range; 35 also works...) to then get the next scene. Next scene is Klein gets sick, Aty comes by nurse him and boost his confidence. Afterwards you'll get a notice to go to 5F of the dungeon and have Klein in your party. NTR route in sight!
Bad news edit: Not sure if Dungeon 5F event will generate if you already cleared the Dungeon well beyond that floor... Still looking into it.