[adult swim] wiki
Cat Ears Headphones-2

In the series FLCL: Progressive Hidomi Hibajiri is regularly seen wearing a pair of cat ears headphones. They were given to her by her father, before he left. They react to her N.O., when she begins overflowing, and turn red while emitting a loud piercing shrieking sound.

In the first episode, Julia Jinyu comments that there's no music playing from them, after knocking them off Hidomi's head. In "Stone Skipping," they drill into her head, causing a change in her personality in the next episode from her usual quiet reserved self to a bubbly, outgoing version of herself.

She comments that despite Ko Ide's opinion, this is her real self, and she uses them to block out the sadness, caused by her father leaving her and her mother.

Canti manages to break the headphones in the final episode, which allows her N.O. to be unleashed transforming her into her robotic self used to fight Raharu.

When the teaser for Progressive and Alternative was aired at Anime Expo in 2017, and artist by the name Wenqing Yan, on Twitter accused Adult Swim of "ripping off" her design for Axent Wear Cat Ear headphones, without crediting her or her permission. Production I.G. would later contact her and agree to give her credit for the design.[1]