My theory with the yacht performance is Michiru expressly invited Haruka/ sent her a ticket. (Haruka goes because she doesn’t REALLY want to have this end with one interaction.)

I imagine Michiru also offers to buy/rent Haruka appropriate attire.

Naturally this offends Haruka to her core. She scrounges up all the money she can, combs through every thrift store, and is just tall enough she can find something relatively nice and cheap that fits her alright.

Except.

RUFFLES.

But she’s so proud, she shows up in a suit she owns and she can show Michiru she doesn’t need her, she’s just fine on her own. That’s all she really needs from the outfit anyway.