Hachiro Oka (岡 八郎, Oka Hachirō) is a highly skilled veteran Gantzer from the Osaka Team, appearing during the Nurarihyon Alien Mission. He was said to have 'cleared' seven times, meaning he scored at least a total 700 points before his death against Nurarihyon.
Oka is a tall, tanned Japanese man. During the Nurarihyon mission he is shown with messy hair. Before the mission he had his hair slicked down and was wearing glasses.
Anzu reveals that there has been a 100 pointer before Nurarihyon that Oka supposedly defeated all by himself after two thirds of the team were killed.
When the Tokyo Gantz team arrives in Osaka, Oka is already in stealth mode hunting for bigger aliens.
Shortly after Tsuneo Nikaido's failed attempt of defending himself against the giant Bull alien, Oka approaches in a mecha with stealth mode and fights it while the rest of the team encounters Nurarihyon. After the Bull alien knocks down the mecha, Oka first attempts attacking the alien with a Z-Gun while riding a hovering Gantz Cycle. After that fails, he jumps off the Cycle onto the alien and to fight it in close combat with the Hard suit.
Just as the Bull alien is defeated, Nurari arrives while chasing the other Gantzers and Oka faces him for a duel while the others escape. The hard suit manages to withstand Nurari's invisible pressure attack, so Oka manages to get close enough for melee. Nurari takes a few blows from the Hard Suit's fists, blade and blaster, then recovers and imitates the Hard Suit. After Nurari manages to heavily damage the Hard Suit, Oka tries to defeat him with a surprise attack from behind.
After recovering once again, Nurari quickly gets bored by the remainder of the Gantz group and leaves to find Oka. Their battle causes the destruction of several surrounding buildings.
Oka loses and dies off-screen, and Nurari returns to the Gantz group with Oka's decapitated head.
Personality and Abilities
Oka is a skilled tactician and hand-to-hand fighter, using his wide range of his equipment in battle.
His prefered method of hunting seems to be using the suit's or mecha's stealth abilities to search out the biggest enemies, leaving the smaller prey to the team.
He is also shown to be an inrecdibly talented melee fighter, despite apparently having no proper training. He could even put up a good fight against Nurari, who considered Kaze's moves predictable (though that may very well be due to Oka's lack in technique).
Oka's strategy and stength worked well enough for him to 'clear the game' seven times, i.e. reaching a total of at least 700 points. At least 100 of these are confirmed to be from a previous 100 point enemy.
He seems to enjoy the hunt, as he stayed in Gantz instead of leaving when he could. Yet, he's level-headed enough to play it safe and retreat when faced with an enemy he couldn't beat.
He prefers to fight alone, shown by both his stealth hunt and duel with Nurari and supported by the flair text on Chapter 270 ("Solitude is like a thick coat."). He never asked for help from the other team members, nor was he shown going out of his way to help others. With his retreat from Nurari, he not only risked losing all points, but the lifes of everyone still present. While he warned them about the danger, he didn't care enough to help them, even unfazed by Kato's pleading.
He takes online Karate classes and played Ping Pong in grade school, both trivia he announced mid-battle against Nurari, possibly in an attempt to mock Nurari by humbling himself.
Oka is shown working as an employee in a bank branch, with his hair slicked back and wearing glasses.
Oka is the first hunter shown with all known advanced 100 point equipment, that being an advanced Gantz suit including palm blasters, a flying Gantz Cycle, a mecha and one Z-Gun. It's unknown whether he owns any other 100 point equipment, considering the shown weapons only amount to 400 of the 700 scored points.
Having reached at least 700 points, he is the one with the highest known Gantz score.
- He may be farsighted, considering he wears glasses in office, but not during the Gantz mission.
- Oka and Nishi are the only ones that are shown to use stealth as main stategy.
- Gantz Manga — Vol. 22 Chapter 256.
- Gantz Manga — Vol. 23 Chapter 259 (p. 21).
Gantz Manga — Vol.
24 Chapter 270.
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- Gantz Manga — Vol. 24 Chapter 272.
- Gantz Manga — Vol. 25 Chapter 276 (p. 14).
- Gantz Manga — Gantz/Osaka (p. 11), Oka isn't explicitly named, but his facial features and the fact that the chapter shows the other members in their daily lifes leaves no doubt.