Your best friend is a Tsundere. And this is obvious.

It's also obvious she likes you. But... Your completely oblivious to it- crazy. I know. But well you two are walking together in the hallway etc etc and nothing much happens. She stumbles a bit but that's much, she then breaks the silence

Mizu:"...We should get something to eat or something... B-but it's not like I asked you out!"

Ah. Classic tsunderes.