Hiyokokko is a small, intelligent, and exceptionally strong baby chicken that lives in a large cage in the school compound with other chicks. It communicates by saying "Peeyo," and only Riku Aoba can understand this speech. Despite its apparent youth, Hiyokokko holds significant life experience and often provides guidance and assistance to friends, encouraging them to find solutions on their own.

The chick frequently assists Riku, and their friendship grew as Riku regularly visited the chicken coop during breaks, sharing his food—especially bread, for which Hiyokokko has an insatiable appetite. Knowledgeable about the city, Hiyokokko has been seen accompanying Riku and another student, Kyohei Dojima, both inside and outside of school, sometimes wearing costumes. It even joined Riku on a school trip.

A skilled martial arts master, Hiyokokko has repeatedly defeated Kyohei in combat. It acts as a protector, stepping in immediately whenever Riku is in danger and capable of confronting multiple opponents at once. The character also put Riku through a rigorous training regimen to prepare him for a baseball tryout with the team captain, Ichiroo.

Hiyokokko functions primarily as a source of comedic relief and resides in the chicken coop at Tsumugino Highschool. Its gender is officially listed as unknown.