Regular bikini. Not water-soluble or see-through-when-wet.
Still kinda cute seeing Kiso react as if it were.
Really, even Kuma wouldn't make her sister showing her breasts. She's a bro level sister, not an seduce-him sister.
Forgive me, I jumped to the wrong conclusion...Your swimsuit suits you well.Well, but still...What's wrong!?Eh, whoaaaa!!That was embarrassing...When did I...!It's...nothing...
Th-thank you...Heeey, you're sinking, you know...eh...?I was in a trance and didn't notice...