First Manga Appearance: Chapter 54
Name Meaning: Oku=interior; to leave behind, Mitsu=honey, Aki=autumn; bright; time to spare
Nicknames: The Bruiser
Gangs: Demon Rider bike gang
Previous Schools: Kyokuto High School
Notable Features: Recently released from jail; a rumoured murderer; leader of the Demon Rider gang
Sometime during Eikichi's junior high years, he arrogantly challenges Kyokuto High & crossed paths with the 2nd year, Okubo, who stabs him in the abdomen, leaving a scar. A Kyokuto High 1st year, Asakura Yoshiaki, later helped Okubo with some money problems sometime in the past. Okubo is later expelled from Kyokuto for murder & served time in juvenile hall.
Upon Okubo's release, Asakura, now a 2nd year along with 2 others come to him for help taking down the Oni-baku after Fumuya's defeat. He demands Asakura's girlfriend, Natsumi, for a night as payment & a reluctant Asakura agrees. He rapes Natsumi inside her room that night as Asakura & his friends stand outside. Upon finishing, he demands another 1,000,000Y as payment from a shocked Asakura.
He forces Asakura to brutally beat up his 2 friends after they decide to bail out on Asakura. He later confronts Eikichi & the Oni-baku Gumi in a restaurant & quickly takes out Saejima. He reminds Eikichi of their past & demands a sum of 1,000,000Y, as well as an apology to Asakura, in order for the Oni-baku to be left alone. A scared Eikichi begs for forgiveness & decides to work out the problem without Ryuji.
He & his friends continue using Natsumi every day, taking photos of her as blackmail, without Asakura's consent or knowledge. Okubo & his friends are later ambushed by a masked Saejima & Makoto, who attack Okubo without Eikichi's knowledge. They are taken down & Eikichi, still injured from his fight with Fumiya, arrives to stop the fight, challenging Okubo one-on-one. They are interrupted by Otsupo & the other 3rd years, who oblige Okubo into postponing the fight 1 week for Eikichi to heal his leg.
Despite promising Otsupo, he decides to break the rules. He rounds up more men & ambushes Eikichi & Makoto at Shonan beach. He knocks down the injured Eikichi with ease. Asakura arrives to help Eikichi for saving his girlfriend, Natsumi from committing suicide but is easily taken down by Okubo. Ryuji, Saejima, Kamata, Tsukai & Abe arrive to help Eikichi & fend off Okubo's friends, allowing a fair fight.
Eikichi eventually overpowers Okubo, despite getting hit in his injured leg by a pole. A swollen-faced Okubo begs for forgiveness but a relentless Eikichi continues his attack. Otsupo & the 3rd year Kyokuto students arrive at the beach & reveal that they are there to prevent Okubo from fighting dirty, to his surprise. Losing the respect of Kyokuto, a desperate Okubo stabs Eikichi in the arm but gets knocked out cold.