Shigoku Kyou

Kyou presents himself as calm and logical while also being incredibly cruel, twisted in nature, and sadistic, as evident by his disturbing fascination with the concepts of life and death. His belief is that the greatest action a human can perform is killing another human, and his primary goal being to kill an individual (whether directly by his own hands or indirectly through somebody else) for absolutely no reason whatsoever.

While he is charismatic and capable of leading the other boys, Kyou has expressed no emotional concern or attachment towards the other four bullies; he didn't hesitate to push Hiro Madoka (someone he's known since elementary school) down a cliff and in the path of an incoming car, something that could've potentially killed him. He also casually gashed Kuga with a pen after the latter pinned him down, permanently scarring him.

After the deaths of the other bullies at Uruma's hands, Kyou showed no visible sadness or concern, even at the thought that he was potentially next; rather he was interested in seeing how that series of events would play out.

Notably, while Uruma was "exorcising the demon" out of Hiro, he called Kyou "the worst demon of them all".

Unlike the other four bullies, Kyou is far smarter and physically stronger than he appears to be. For example, it was mentioned that he was a prodigy at a local school and that he won a black belt in Judo, making him one of the most powerful people in the story. Later on, it's revealed that he also has a group of supporters who may or may not be just as bad as him, showcasing a highly manipulative and charismatic aspect of him akin to that of a cult leader, able to make ordinary people succumb to their worst impulses and follow him blindly and loyally. This shows that Kyou is already far worse a threat than he appears to be.

It's shown later on that Kyou isn't without capable of showing shock when something unexpected happens that interferes with his plans. He was notably annoyed when Uruma's grandfather interrupted their experiment and freed Kakeru, and even showed noticeable fear for the first time when he killed one of his minions swiftly.

Shigoku wants to find a new entertainment besides bullying other children. He noticed a very attractive person at school, who, surprisingly, was able to attract his attention. And in pursuit of this personality, he forgot a little about his gang of hooligans, giving them the go-ahead for self-indulgence.