Ah, it's nori. "Nori" is Japanese for edible seaweed, but it is used to refer to the top piece of a bikini in this series.

Elder sister Fusou.

Let us both get our Kai Ni together.

Seaweed?

Nee-sama, I'm satisfied with getting this for my Kai Ni.

Hang in there, Yamashiro... (tears up)

Soy milk hotpot is tasty... Literally says "Miruku Nabe" here

Please don't say it's just some unlucky souvenir.