Tzuyu likes Sana. Literally, everyone and their grandparents know... well except for the person that Tzuyu actually likes of course. 

“She's so dense. Ugh, how do I even talk to her if she doesn't even know I exist???”

“Tzuyu. I’m pretty sure everyone in this school knows you exist..”

“So what? She doesn't. So what's the point even”

“What are you gonna do now?? Make me talk to her and find out about her??”

Tzuyu had an epiphany. Her face showed it, her epiphanies weren't always bad but this one... Dahyun had a gut feeling it was bad. Superbad.

“You’ve gotta be kidding Tzuyu...”

“Dahyun.. you're my bestest buddy, r-right? Please?? For me?”