Cameo Appearances

Aka-senpai and Buru-senpai
Aka and Buru appears in many of the backgrounds in Pinku-Chan no Sekai. They are seen Because of Monaikochan's Graditude for a YT User Letting her use a Story she once made.

Produce-chan
Produce-chan is seen in the Crowd in all the Episodes where Rainbow Souls is Performing. It is confirmed in Episode 1 of season 3 that she is a Korean Pop singer and that She is a Tofuhead. It is also Confirmed in that same Episode that she is Hatty's Favorite KPop Singer. Produce-chan is also a Reference to Produce 101 and 48.

Hatty Hattington (Original)
So, Hatty from Pinku-chan No Sekai is an Anime recreation of Hatty Hattington from Battleblock Theater. So in some Episodes, (Mainly Rainbow Superstars and Po Pi Po), He is seen behind the Curtains of the Auditorium. He is also seen once Bopping (PCNS) Hatty in the Head for Stating his favorite KPop Singer (Produce-chan) is a Tofu.

Fletcher Raitoningu
Fletcher first played a roll in episode 1 of season 2. He was the substitute. Fletcher later started appearing in the backgrounds, usually seen with Aka and Buru. Fletcher, along with The Creator, sometimes even appeared before they were introduced.

The Creator/Creator-Chan
The Creator was first seen in the season finale of season 1. The Creator was said to know all of the secrets of the universe. After giving up on the journey, The Creator also started to appear in backgrounds.

Fletcher Sekai
Ideku-Chan appears in backgrounds. He also appeared in episode 5 to do the spell for Pinku-Chan and her friends. He did not appear in any other episodes.

Shingu-Chan
Shingu is a character that appears in the background. Shingu also looks identical to a Toad.