Koba

Koba is calm, logical, cunning, and sadistic. He prefers methods that let him control the pace of a fight and appears to enjoy watching opponents realize that their own movement is accelerating the poison killing them.

He readily uses underhanded tactics and has no moral concern about putting hostages at risk. Although the assignment revolves around capturing politically valuable targets, Koba is willing to deploy poison capable of killing everyone trapped with him.

His relationship with Higuchi is comparatively relaxed. Koba jokes about his partner's belief in virtue points, suggesting that the two have worked together long enough to understand one another's eccentricities.

Koba produces a colorless and odorless poisonous gas inside his body. Once inhaled, the poison causes extreme pain and becomes more effective as the victim's heart rate rises. Excitement, panic, and physical exertion therefore accelerate the process.

He is immune to his own poison and carries an antidote for allies.

Koba deliberately supplements the gas with an assault rifle and throwing knives. By forcing poisoned opponents to dodge, run, and fight, he causes their heart rates to increase and makes the toxin work faster.

He is also an accomplished direct combatant, capable of reacting to Sakamoto, Rion, and Nagumo despite relying primarily on poison. His recorded bounty of ¥600 million reflects his reputation.

Koba appears during the bodyguard mission in Sakamoto's past, where the young assassins are escorting the JAA chairman's wife and daughter.

Higuchi attacks first while Koba remains concealed, allowing the group to focus on the more obvious threat.

Koba eventually traps Kindaka, Nagumo, Rion, Uzuki, and the protected civilians inside a confined tunnel and fills it with poison gas. The situation becomes especially dangerous because fighting him directly accelerates the toxin.

Sakamoto returns to the confrontation after defeating Higuchi. By minimizing unnecessary movement and exploiting an opening, he eventually gets close enough to choke Koba, ending the poison attack.

Kindaka survives the poison but later falls into a coma lasting more than eight years, giving Koba's attack consequences that extend far beyond the original mission.

Higuchi is Koba's assassin partner. Koba trusts his fighting ability while teasing his belief in virtue points.

Taro Sakamoto becomes Koba's decisive opponent after returning to the poisoned tunnel.

Yoichi Nagumo and Rion Akao attempt to fight Koba while deliberately limiting their physical exertion.

Kindaka is poisoned during the confrontation and later falls into a prolonged coma connected to the toxin's effects.

Kei Uzuki is trapped alongside the others during Koba's attack.

Ai Amo and Konomi Amo are the protected members of the chairman's family endangered by Koba's poison.