Speaking of main girls, who of the 5 was the girl in the hat and dress at the park with Fuutarou?
Hair-lengthwise I thought it was Nino, but she seemed genuinely oblivious to the whole thing. Yotsuba had eerily perfect timing, but she's not the type to sneak around in the middle of training. Ichika seems likely due to her acting chops, but what was said to Fuutarou was too cruel, even for her.
Miku's good at impersonating people, but she wouldn't want to hurt Fuutarou, while Itsuki is too innocent to be able to put on an act like that towards someone she's very familiar with.