大概是只存在于幻想的情节，或许是架空现代if背景，两个人夏天穿着泳装去玩水。
先代：唔啊，稍微有点紧啊…啊咧，这个带子…
瑞灵：喂喂，这不是要松开了吗？
先代：哎哎哎哎？（手忙脚乱）
瑞灵：穿白色泳装下水，你真是有够勇敢…风格倒是很适合你。
先代：欸？嘛……瑞灵的黑色泳装很可爱哦！
瑞灵：嘛……我只是因为实用才选了这件，中看不中用的泳装实在太多了啦

It's probably just a fantasy scenario, perhaps set in an alternate modern world, where two people go swimming in swimsuits in the summer.

Sendai: Ugh, it's a little tight... Oh, this strap...
Mizuchi: Hey, aren't you going to loosen it?
Sendai: Hey, hey, hey, hey? (flustered)
Mizuchi: Wearing a white swimsuit in the water, you're really brave... but it suits you well.
Sendai: Huh? Well... Mizuchi's black swimsuit is cute!
Mizuchi: Well... I just chose this one for practicality. There are too many swimsuits that look good but aren't functional.