Per wiki policy, Spoilers Off applies here and all spoilers are unmarked. You Have Been Warned.

Mayu's constant changes whenever she drinks a different drink (ex: turning into a pig when she drinks meat soup).
From Chapter 3:
Mayu: [after they fell off a cliff] Amamiya! Amamiya!! Are you dead?!
Amamiya: Idiot! Don't presume I'm dead!
When Mayu drinks a super fighting drink that turns her into a boy. And "Boy Mayu" challenges Amamiya to win Mayu.
To get Nazuna and Ryouta to meet together, Mayu and Amamiya each give them a letter to meet up with the latter. Ryouta's reaction?
Ryouta: A love letter from Amamiya...?
When Mayu attempts to hit Nazuna with a love arrow to get her to fall in love with Ryouta, it accidentally hits Konoha, who falls for Mayu.
Konoha: Mayu-san! It's pure love between us! ♡
Mayu: [runs away] Kyaaa!!

Funny / Pixie Pop