- 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.
- She says and does some of the most epic things in the game.
Before St PigeonationsEdit
Eight years before 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 seeing Hiyoko's dead parents and witnessing the incident, were approached by Shuu. Shuu asks 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 of "I would do anything to make Ryouta's wish come true."
Hiyoko was killed in the start of the Hurtful Boyfriend route by the Charon Virus in Ryouta. The deadly virus that affects only humans was part of Shuu's plan to fuilfill Ryouta's wish - with the human race gone, the fighting will stop. Shuu then had Yuuya cut her up into pieces, and he removed her brain from her body and put 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 attempts to impede Ryouta and co from entering the sealed labs and keeps every other normal student away from the main building as Ryouta and Sakuya investigate.
Labor 9 is a prototype of the Labor Model New Humans that was first developed by Dove Party researchers, but condemned as unethical and the project shut down. It was made to assist birds, and with 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 uses a tazer to short Labor 9 to get to Shuu.
Even dead, however, Hiyoko's spirit lives 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 lay frozen in cryogenic slumber to wait for a cure for the Charon Virus.