Headcanon that Yuu likes to play with Mika's hair since it's so fluffy. Mika is slightly annoyed by this but still lets Yuu play with it.
Yuu: *starts stroking Mika’s hair*
Mika: this again, Yuu-chan?
Yuu: I don’t understand why it bothers you. Your hair screams for me to touch it! *stroking intensifies*
Mika: … *blushes furiously*
Yuu: did you just-
Mika: I TOLD YOU NOT TO PLAY WITH MY HAIR