Spoiler for On the Orimura siblings and Pika-tan:
I think there is a mutual brocon-siscon going on with the Orimura sibling. One how the heck did Chifuyu sense where Ichika and Charllote was in a changing room? Two Chifuyu wears a provocative black bikini that Ichika dumbly stares at. Charllote acknowledging the greatest rival is in fact the Elder Sister!
Oh Pika-tan wearing that suit in the beach. It also moves its tail! She may be on the same wavelength as Tabane with the bunny ears.