From the thumbnail.

I thought it's Yuuka & her bug friend :P

She Look kinda Yuuka here..

killyou5 said:
She Look kinda Yuuka here..

Thought it was as well.

How can they breathe if they're underwater?

Lol101 said:
How can they breathe if they're underwater?

sponges shaped like ppl? lung replacment surgery? no laws of physics in fanart?

Arayuth said:
From the thumbnail.

I thought it's Yuuka & her bug friend :P

I thought the same but I don´t believe it can be part of that pool for the misleading thumbnails just for that.
On a closer look, our spongie friend is still scary as hell, even in human form.