The text ぴょん (pyon) is an onomatopoeic word in Japanese that mimics the sound of a rabbit hopping or a playful bounce. It’s often associated with rabbits and their cute, energetic movements.

In this context, the rabbit holding up the girl’s hair to make it look like animal ears is playful, and ぴょん adds to the lighthearted, bunny-like atmosphere of the scene. It’s as if saying, “Hop!” or “Boing!”