In-game Description

JP: [VACATION♪]坂東美久龍
「もしかしてみんな、気合の入った水着持ってきたのか！？」

EN: [VACATION♪] Bandou Mikuru
"Could it be everyone brought their best swimsuits!?"
気合 (kiai) means "effort" in this context. Everyone put in effort to decide what swimsuit to wear except Mikuru, who brought a school swimsuit. The bikini in the image was picked out for her.