- "From now on, except my allies, all of you are 'Witches'!"
—Aguni in the manga Chapter 21
Morizono Aguni is a character first appears in the Beach arc and the leader of the "martial sect" of the Beach residents.
Aguni's father was a sore loser and problem drinker. He constantly abused his son and wife after returning home carrying another drink. To draw the attention away from his mother, the frightened Aguni retorted his abusive father but his mother did not stay long in their home. Aguni also ran away from his father when he was 12 years old.
Aguni and Takeru Danma (Boshiya) had been sworn friends when they were 16 years old. Both messed with bunch of street thugs but easily crushed them with just 2 men. Turning 17 years old, Aguni probably wanted to beat his father for revenge, only learned that he died of acute alcohol poisoning half year after Aguni's leave.
After winning some games, Aguni helps Boshiya to establish the utopia by keeping the trouble makers under control so they do not disturb the equilibrium of the Beach society, a role he agrees to assume until Boshiya murders the residents for hiding the cards which should be handed over for the society. Disappointed by Boshiya's heightened spirit of brainwashing the residents with the false method of departing the Borderland, Aguni calls out Boshiya right after the latter has just been returning from game and bids farewell. Boshiya points his gun on the back of Aguni but he quickly shoots back and kills him, only learns that Boshiya's gun is not loaded. He finally understands that Boshiya has been concealing his fear of being unable to escape the Borderland. Boshiya would rather die in his best friend's hand than by anything else.
Aguni is devastated. When the Ten of Hearts begins in the next evening, he orders his underlings to murder anyone not in their sect, making them believe that they are merely doing what the game requires them: Throw the "Witch" into the bonfire before timeout. The fact is, Aguni wants to lead everyone to game over so all Beach residents, including himself, are buried with the false hope spread by Boshiya. Even hearing Ryōhei Arisu's revelation of his true motives and reasoning, Aguni still claims himself to be the Witch and delays everyone else to proceed. His rampage is only distracted when Asahi attempts to reveal her true identity as the dealer which activates the blazing laser of execution. The game has been cleared, but the Beach resort is destroyed in fire set by Niragi. Aguni hides himself from the crowd, probably out of guilt.
- Aguni's alias coincides with the Japanese rendition of the Vedic supreme divinity of fire, Agni.