Hajime Kokonoi/Synopsis

History
When Koko was younger, he was deeply infatuated with Inupi's sister, Akane, even though she was older than him by five years. One time, he tried to kiss Akane when she was asleep in the library, but he was caught. Koko later confessed, which prompted Akane to wait for the both of them to get older for marriage.

However, a huge fire broke out in the Inui house one night. Disregarding everything, Koko valiantly rushed into the house, saving whom he thought was Akane, but turned out to be Inupi. As a result of the fire, Akane suffered severe burns and fell into a coma. The treatment would be 40 million yen, which was a price not even Akane's parents could afford. For this reason, Koko did everything he could to learn about finance so he could save money for her treatment plans. He realized that the fastest way of gaining was to turn to crime, so he recruited delinquents to do his bidding. However, everything would later come for naught as Akane had succumbed to her injuries and passed away. As a result, Koko became even more money-crazed afterward to try to fill in the void that was caused after Akane's death.

Valhalla Arc
Koko first appears as a Tokyo Manji Gang Top Admin in a present timeline during a meeting with Toman's top members. Shuji Hanma shares that Koko's public business and Hakkai Shiba's corporate front, among others, have been searched by the police three days prior, and believes that the culprit is among them. Haruki Hayashida believes otherwise, which leads Koko to argue with him.

Black Dragon Arc
Back in the past, Koko is outside the Shiba residence with the 10th Generation Black Dragon. He welcomes Hakkai home, then spots Takemichi Hanagaki with Hinata Tachibana and gets furious when he learns that a Toman member has stepped foot on their territory. He threatens to kill him per their leader's orders.

Koko next appears with Seishu Inui in a meeting between Taiju Shiba and the First and Second Division leaders of Toman. Later, Koko appears at a karaoke bar to snuff out a mole from Black Dragon, who meets with Takemichi, Chifuyu Matsuno, Tetta Kisaki, and Hanma to sell out Taiju's whereabouts in exchange for cash. Koko summons his subordinates and orders them to take the mole away, then makes a deal with the captains to disclose whatever they wish to know for ¥100,000. Kisaki obeys and asks when Taiju is alone. Koko tells him that Taiju is only ever alone on Christmas day at church, then leaves excitedly with anticipation for Christmas.

On Christmas day, Koko individually fights Takemichi and spectates the main fight between Taiju and Manjiro Sano. After Taiju is defeated by Mikey, Koko withdraws to call the aid of the Tenth Generation soldiers outside. To his surprise, Ken Ryuguji has beaten all their members, declaring Black Dragon's lost against Toman. As the battle ends, Koko follows Inupi after bidding Taiju goodbye.

After New Year's Day, Koko and Inupi attend a Toman meeting and introduce themselves as the leaders of the new 11th Generation Black Dragon. Mikey assigns them under Takemichi's division and Koko delightedly greets him.

Tenjiku Arc
In an alternate present timeline, Koko leads a group of Toman members to intervene a meeting between Takemichi, Taiju, and Naoto per Izana Kurokawa's orders.

Koko is later seen held hostage by Yasuhiro Muto along with Takemichi and Inupi. Koko claims that Takemichi is not Tenjiku's mole after being suspected of betrayal by Toman's Fifth Division. Much later on, Mucho discloses that he is the real mole all along, and that he has been acting as Tenjiku's spy since its formation. He was also instructed by Izana to recruit Koko into the gang, for he saw Koko's financial ability as an asset. Koko initially rejects the offer, but he eventually accepts it under the condition that Takemichi and Inupi are let free.

During the Kanto Incident, Koko interrupts a physical fight between Inupi and Mucho to take on Inupi as an opponent alone. Inupi tells him to come back to Toman since he was coerced into joining Tenjiku in the first place. However, Koko refuses because Toman cannot give him money. He invites Inupi to join him in Tenjiku with a guaranteed position in the gang, but Inupi refuses out of respect for Takemichi. When Inupi mentions Koko's obsession with Akane Inui, they begin to fight. Koko claims that he now lives for money and spirals into a series of flashbacks remembering Akane.

Koko continues to fight Inupi as the latter tries to wake him to his senses that Akane is now gone, hence there is no need for him to keep saving money. Koko vents out his frustrations to Inupi through kicks and punches, and explains that, even though there is no need to save money for Akane anymore, he has proven himself to be an asset to various people like Taiju and Izana, making it complicated to give up his monetary obsession. Inupi disproves, but Koko stops him by momentarily imagining Inupi as Akane, and wonders how she would react to his behavior if she was still alive. With this, Koko admits that he is aware of Akane's passing and tells Inupi that he cannot undo his illegal ways since he had dedicated himself to Tenjiku, before Mucho interrupts the fight.

When all of Toman has been knocked out except for Takemichi, who is battling Kakucho one-on-one, Koko states that Inupi was idealistic when he claimed to see the future of the Black Dragon in Takemichi's hands. While Takemichi is being beaten up, Koko points out that the reality is Toman's loss and Tenjiku's win. However, he is surprised when Takemichi refuses to give up after getting beaten badly.

For the rest of the fight, Koko spectates from the audience. He escapes from the pier in time before the cops arrive.

On the day of Emma Sano's funeral, Koko meets Inupi briefly. He tells him that he will now go his own way and advises Inupi to not go down the wrong path without him.

Bonten Arc
In a present timeline, Koko is introduced as a Bonten Executive alongside the other top members.

Three Deities Arc
In 2008, Koko is introduced as a member of the Kanto Manji Gang.

On the night of Tanabata, Koko is with Mikey in their office, asking him if he is alright. Later in the night, he goes to the Battle of Three Deities with the gang to fight against Brahman and Rokuhara Tandai. For the duration of the fight, Koko stands beside Mikey to spectate. He indirectly asks Mikey whether or not he cares about Ken Ryuguji's death.