- Her name, "Hiyoko," means "chick" in Japanese.
- She's often depicted by the fandom as a girl wearing a fake yellow chick head or a rock pigeon head in a futile effort to blend herself in the school full of birds, or as a normal girl with brown shoulder length hair. Moa, Hatoful's creator, has said that Hiyoko's image is up to the fans' imagination.
- She has a huge range of special attacks and some are powerful enough to break things.
- Her childhood pigeon friend, Ryouta, is in love with her, but she's too dense to figure it out.
Before St. Pigeonation'sEdit
Eight years before the events of the game, both Hiyoko's parents were shot and killed in the Hatoful House incident when they tried to act as mediators between the human radicals and birds. Their deaths signaled the end of negotiations and started an all out fight between riot police and hostage takers in Hatoful House.
Hiyoko and Ryouta, while witnessing the incident and the deaths of Hiyoko's parents, were approached by Shuu. Shuu asked if they had any desire, any wish to be granted. Ryouta wished for world where humans and birds don't fight. Hiyoko then added the fatal line, "I would do anything to make Ryouta's wish come true."
Hiyoko was killed at the start of the Hurtful Boyfriend route by the Charon Virus in Ryouta. The deadly virus, which affects only humans, was part of Shuu's plan to fullfill Ryouta's wish - with the human race gone, the fighting would stop. Shuu had Yuuya cut her up into pieces, himself removing her brain and putting it in Labor 9, a scarecrow-like being. Her last gasps to Ryouta before she died were eerily echoed by Labor 9 as, under the control of Shuu, it attempted to impede Ryouta and company from entering the sealed labs. It also kept every other normal student away from the main building as Ryouta and Sakuya investigated.
Labor 9 was a prototype of the Labor Model New Humans that was first developed by Dove Party researchers, but was condemned as unethical, and the project shut down. It was made to assist birds, and as a human brain controlling an artificial body it was capable of tasks that bird limbs would find difficult to do. Shuu has continued with the Dove Party's research and created and used Labor 9 as his sidekick. Ryouta eventually used a taser to short out Labor 9 to get to Shuu.
Even in death, however, Hiyoko's spirit lived on. She appeared as a green floating flame to persuade Ryouta when he went into a brainwashed berserker state, and accompanies his spirit as he lays frozen in cryogenic slumber as he awaits a cure for the Charon Virus.