The No Longer Human serial killer of Kyoto and member of the Zerozaki clan: Hitoshiki Zerozaki. Notoriously known as the Prowler during the Kyoto serial murder case. Hitoshiki is a man with a small stature that kills for the sake of killing. Soushiki Zerozaki and Hitoshiki have a somewhat brotherly relationship, though they've grown distant. In general, he doesn't have many friends as a serial killer, though Iori Mutou could be considered one, as well as Ii. Another killer, Izumu Niounomiya, is a friend and rival of Hitoshiki.
Hitoshiki himself is eccentric, though he generally has a casual personality and way of speaking. He considers himself a brat and believes everyone else was once a brat. When he and Ii meet, he calls Ii a doppelganger as they are essentially identical, yet so different. Hitoshiki is later described as the mirror image of Ii, and what Ii would be like if he didn't hold back. As a Zerozaki, Hitoshiki has a desire to kill anyone he meets without remorse, though he is capable of holding himself back. Like Ii, Hitoshiki has a catchphrase where he often says, "What a riot," which contrasts against Ii's "Nonsense."
As both a Zerozaki and a serial killer, Hitoshiki has a couple abilities and tools at his disposal. In the vest he wears, there are many knives placed all throughout it, which complements his mastery at using knives. To go along with his knife expertise, Hitoshiki is also able to utilize string, making a nearly undetectable trap. Unfortunately, with all his prowess in killing, he cannot do much against Ii, as they can counter each other and will just end up in a stalemate.
Hitoshiki's knife finesse has made him able to hold his own against Jun Aikawa. Despite this, he cannot defeat her, thus he escapes. The two later come to an agreement where Hitoshiki vows to stop killing to continue living and tells Jun Ii's solution to his own problem during the time.
When Hitoshiki was born, his parents both died. His parents were Hataori Zerozaki as his mother and Zeroshiki Zerozaki as the father. As they died after Hitoshiki's birth, Soushiki began to raise him.