|BIM Type||Blazing gas|
|Japanese VA||Yasuhiro Mamiya|
|English VA||Mark X Laskowski|
"Unforgivable... Absolutely unforgivable… Then… I'll be the one to punish all of them…" — Mitsuo Akechi
Mitsuo Akechi (明智 光男 Akechi Mitsuo) was a player of the real-life Btooom! game. He was formerly part of a group comprised of Himiko, Masashi Miyamoto, Isamu Kondō, and himself, but later had a falling out with the group. He later attempted to rape Himiko but was killed by her in self-defense.
Mitsuo is a bespectacled, obese man with a round head and very small eyes. He sports short black hair slicked around his forehead. He wears white ¾ pants and a black t-shirt. His shirt displays the word "REBOUND", with a star in the "O". He carries a small shoulder-strap satchel. Like any player in the real-life Btooom! game, Mitsuo has an IC chip implanted in his left hand and a bandolier, which he wears on his waist.
Mitsuo is a cowardly, yet vindictive man. He, at first, is seen as a docile man, as he avoided conflict involving himself. It is later revealed that he is unhesitant toward engaging in conflict so long as it is to his advantage, such as setting up an ambush, and is quick to impose his beliefs on others, especially when pressured. He is also extremely ignorant, with his perverted nature spurred on by such ignorance. He is misguided by the belief that all women enjoy sexual pleasure, which he bases on various ero-manga and ero-games.  Although he states that he'll protect Himiko, he attempts to exploit her for his own benefit, revealing his hypocritical nature. His oppression of women is based on the justification that a woman is obedient when she can no longer reject him, especially since he is sensitive of his appearance, regarding himself as an obese, unattractive, and unhygienic man. 
According to Mitsuo, he engaged in sex with a girl he liked once, though this garnered a lot of hate for him, even though he claims she didn't oppose his advancements.
On the morning of the first day, Mitsuo, along with Masashi and Isamu, awake a sleeping Himiko. Upon Isamu's invitation, Himiko joins their group. After a conflict between Isamu and Masashi, which resulted in Himiko resisting after being taken hostage by Masashi, Mitsuo argues that their weapons are responsible for their conflicts. He then proposes they elect a leader to watch over their weapons. The group agree on Himiko as leader.
At noon, Mitsuo, along with Himiko and Masashi, investigate the location of a parachuted supply case dropped by a cargo plane. After obtaining the supply case, they proceed to open it, discovering various items inside, including food and water. They then begin to consume the food and water. However, upon Isamu's appearance, their actions are quickly opposed by him. As Isamu explains the importance of rationing, Masashi slits Isamu's throat with his combat knife from behind. Isamu later succumbs to his wound. Soon after, Isamu's IC chip is possessed by Masashi.
On the morning of the second day, Mitsuo wakes Himiko to escape with him, along with all of the group's BIMs and supplies. As they proceed to escape through the jungle, Mitsuo stops to rest. However, after sending a sonar wave, he realizes Masashi is pursuing them, prompting him to run in order to elude Masashi. Once at a nearby bridge, Mitsuo has doubts on whether he'll be able to cross the bridge due to his weight. Unfortunately, Masashi arrives to confront the two as Himiko crosses the bridge. As Mitsuo and Masashi talk, Masashi learns of the radar's existence. Masashi then attempts to advance upon them, however, he soon retreats after Mitsuo hurls a blazing gas BIM in his direction. Mitsuo then crosses over the bridge to safety.
After eluding Masashi, Mitsuo, while holding Himiko's hand, suggests to Himiko they set up an ambush to attack other players, though Himiko questions his plan. When Mitsuo refuses to let her go, the two struggle, ending with Mitsuo stunned by Himiko's taser. As Himiko leaves with both the BIMs and the supplies, Mitsuo swears he'll punish her. Sometime after, Mitsuo manages to utilize the radar to track Himiko down. Himiko attempts to flee, though Mitsuo restrains her with his weight. He then proceeds to sexually assault her while revealing of his history with a girl he had once had sex with. Once Himiko ceases to resist, Mitsuo takes it as a sign of her complying, and proceeds to take off his pants. Himiko then attempts to use her taser, though Mitsuo disarms her. Before Mitsuo attempts to rape her, Himiko activates a timer BIM, prompting a fearful Mitsuo to flee. As Mitsuo flees, Himiko hurls the BIM in his direction. Just as Mitsuo takes notice of the BIM, the BIM explodes, killing him.
Equipment and Skills
Blazing Gas BIM
- Mitsuo used one to protect himself by creating a diversion.
- Amount used: 1
- He used one in order to protect himself from Masashi on the second day.
- These BIMs were stolen from him by Himiko after she defended herself from him.
Due to his obese figure, Mitsuo is capable of subduing his foes with his overall weight, however, he is unable to handle any significant amount of physical exertion and will often sweat as a result.
- Btooom! manga, chapter 34, page 25
- Btooom! manga, chapter 33, page 27
- Btooom! manga, chapter 34, page 24
- Btooom! manga, chapter 32, page 21 and anime episode 2
- Btooom! manga, chapter 32, page 28 and anime episode 2
- Btooom! manga, chapter 33, page 19 and anime episode 2
- Btooom! manga, chapter 34, page 34 and anime episode 2
- Btooom! manga, chapter 33, page 15-19 and anime episode 2
- 'Btooom! manga, Chapter 14, page 3
- 'Btooom! manga, Chapter 49
- 'Btooom! manga, Chapters 59-60
- 'Btooom! manga, Chapter 30