Hajime Kokonoi/Synopsis

History
When Koko was younger, he was deeply infatuated with Inui's sister, Akane, even though she was older than him by 5 years. One time, he tries to kiss Akane when she was asleep in the library, but Akane caught him. He confessed, and Akane agreed to wait for them when they became older.

However, tragedy struck. 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 Seishu. 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.

Thus, Koko did everything he could to learn about finance so he could raise money to save Akane. He realized that the fastest way was to turn to crime, so he recruited delinquents to do his bidding. Everything was for naught, for Akane eventually succumbed to her injuries. Coco became even more money-crazed afterwards in order to try to fill in 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 command and Koko delightedly greets him.