Going back and rereading the first chapters, rather than going "hurr, dumb tsundere", I feel bad for Rimu.
She already realized (
back in chapter 2) that intellectually, she knows she can't keep Takeshi's power (and his hands) to herself, but emotionally, she
hates it. With that first boob-fondling orgasm no doubt came a rush of brain chemicals including enough oxytocin to convince her to pair-bond with this male RIGHT NOW. But once that train-ride-home brain warm-fuzzy wore off, the reality that she'd inevitably have competition sunk in.
It's no wonder she's so meddlesome: as much as her brain wants Takeshi to realize his dreams of helping people, her heart isn't just jealous, but
afraid of losing the crush she made as soon as another young woman her age gets drunk on the coom-chemicals from a session of magic-skill-enhanced-oppai-fondling.
To paraphrase Douglas Adams, part of being an adult is the ability to hold two contradictory views at the same time and be able to accept it, and poor Rimu got thrust into that situation quite quickly.