Chaos is first introduced as a human fan of wrestling, named an 'otaku' by the other characters for his obsessive love of chojin and their culture, and is seen to be prone to panic attacks, as he endures flashbacks of a traumatic past. He is later revealed to be a Time Chojin, who is instrumental in Mantaro's success and saving the life of Kevin Mask.
When the Time Chojins used their "Legend" Destroying Bell, he suffered along with the other Chojin. He is the lone survivor of the massacre of his parents and fellow villagers. Remembering this incident causes him to go into violent fits, at which point he has to take a sedative (in the form of an asthma inhaler). During these fits, his fighting strength increases many fold, and he is able to compete at the same level as Neptuneman. After taking his medication, however, he forgets everything he did during his fit.
He works as a bogus Chojin Wrestler named Butanikuman (ブタ肉マン, Porkman), putting the money he earns into the Gakincho House orphanage he grew up in. Chaos has feelings for Rinko, although he also has a huge crush on singer Matsuda Seiko and has a collection of her merchandise.
Chaos is a very kind, although somewhat childish, character. He claims to be a human and not a Chojin. Chaos is a huge Chojin Otaku, and has a huge collection of Chojin-based goods (including Kinkeshi figurines). He will go through any means to add to his collection, even beat up his friend Kawazaki-kun.
He also has an odd obsession with pigs and giving people pig-themed gifts, most probably due to the fact that his earliest clear memory is living with a huge pig. He appears to greatly admire Idol Chojin Geronimo as a fellow "human fighting alongside Chojins".
A horn grew on the side of his head, as a child. Currently, the horn is gone and in its place is a keyhole shaped hole, which is a characteristic shared with the Time Chojin (he also has a design pattern on his body similar to them). He has long blond hair and pale skin, with a muscular physique.
Chaos grew up on Planet Avenir. 
He was trained by his father - the king - in Chojin Wrestling, and on his sixth birthday was gifted with Chaos' Memory Key.  One day, Thunder and Lightning attack his village and kill everyone in his village, which includes his mother and father before his eyes.  Due to his parents providing a distraction, he is able to escape into the woods and find Horae Avenir's grave, where promises to avenge them someday and allow the Avenir Clan to live on, and rips off his Time Horn to travel through time. 
The strain from being so young, and untrained, means he loses his memories and travels seven years previous to the intended time of Thunder and Lightning's arrival in the Ultimate Chojin Tag Tournament.  This causes him to land outside of Gakincho House, where Sister finds him sleeping underneath a huge pig.  The pig looks at Sister and then walks into the woods, never to be seen again.  Sister then took Chaos to Gakincho House and raised him as her own, due to Chaos having amnesia.  Over the years he gets stronger and helps Sister raise the orphans. 
The orphans love him dearly and refer to him as An-chan (あんちゃん, Big brother). 
He uses his Chojin otaku knowledge to get a job with a bogus Chojin Wrestling show as Butanikuman.  He spends his money on gifts and food for the orphans, or on his collection of chojin items and otaku goods. In 1983, he and his friend Kawazaki-kun attend the Universal Chojin Tag Tournament.  After Neptuneman flies into space and explodes, Chaos obtains the Kinnikuman Great mask. Kawazaki-kun is actually the first to grab the mask, but Chaos smacks him around until he gives it up. 
Chaos first appears in an exhibition match. 
He appears dressed as "Butanikuman", in a match with humans pretending to be chojins. They stick to a script, but - with Mantaro's encouragement - Chaos starts to fight off-script. He loses as intended, until a pair of brass-knuckles flies out of the ring and strikes Rinko Nikaido.  This causes him to attempt a double-Kinniku Buster on the men who causes Rinko to be harmed.  This reveals his true form beneath his costume, which is highly attractive and muscular. The other 'wrestlers' then attack Chaos.
Mantaro joins in the ring to defend Chaos, and together they manage to defeat all the others. This leads to Chaos being fired from his job as a 'wrestler'. While Mantaro believes Chaos to be the chosen chojin that will save the world during the Time of Peace, Chaos is seen collecting Kinkeshi and reading manga, as they follow him to his home through the forests.  He spots them and offers them and offers them to come home. 
Chaos takes them to Gakincho House, deep within the mountains, and Rinko convinces him to invite them for dinner. It is revealed by Sister that Chaos is an orphan, like the other children in Gakincho House, and that he uses the money he earns as a 'wrestler' to help pay towards the other children. After dinner, they enter his bedroom and find that he is an otaku with a vast collection of chojin goods. Chaos explains that he cannot help them, as he believes himself to be human.  Rinko convinces him to join the Muscle Brothers Nouveau. 
Mantaro Kinniku finds the Kinnikuman Great mask in Chaos' room, in Gakincho House. They decide that Chaos will wear this mask to pass as a chojin and sneak into the Ultimate Chojin Tag Tournament.  They enter the tournament as Entry #15.  Chaos is nervous and enters carrying a bag, in which he carries a video-recorder to capture the moment, and follows this by tripping on his entrance into the ring, where he falls onto the canvas.  Robin Mask helps him to his feet, and Chaos offers him an action figure in thanks.
Chaos - as a fan - proceeds to take autographs from various chojin, as well as take photographs with them, and finally he takes an imprint of Mongolman's face, which angers the other chojin.  A battle royale is then announced.  Chaos does not participate for a long while, and instead sits on the sidelines to make Kinkeshi of the Hell's Bears.  Thunder then attacks Chaos to make him stop making kinkeshi.
To everyone's surprise, Chaos manages to masterful evade every attack.
After he kicks Thunder away, Thunder proceeds to break his Kinkeshi. This leads Chaos to attempt a rolling savate, which is swiftly countered, and a Kinniku Buster upon Lightning, which he fails despite previously having accomplished the move during exhibition matches. Lightning and Thunder manage to leave Chaos on his knees, bleeding profusely, after a series of brutal attacks.  Mantaro intervenes and - while holding Chaos - manages to counter attacks and protect Chaos. 
Chaos tries to leave, but Mantaro begs him to stay for Kevin Mask's sake. They formulate a plan to constantly run from their opponents to avoid being attacked, and hopefully remain one of the last standing, thus winning by default.  On seeing The Alphabet murdered, Chaos suffers a flashback to a burning village from his childhood, and - in his panic attack - only his inhaler can help soothe him. 
Neptuneman then attacks Chaos. Chaos manages to counter, and - with Mantaro's help - commits a German Suplex against Neptuneman.  Neptuneman then tries to take Chaos in an Optical Fibre Cross-Bomber, but Mantaro intervenes and saves him by throwing Seiuchin's helmet to block the attack.  After Mantaro accidentally scares Great, Great suffers another panic attack and faints outside the ring.  The battle royale is then announced to be over, and Muscle Brothers Nouveau win as one of the remaining survivors. 
Chaos is left bedridden from his injuries. 
He overhears Meat Alexandria tell Mantaro that he disbelieves Chaos is a suitable teammate, and - through his tears - Chaos abandons his mask and escapes through a window.  He returns to Gakincho House and attempts to destroy his chojin collection, but Sister comes upstairs to talk with him, and she brings with her Chaos' Memory Key.  Sister reveals that he was found clutching the key, with a keyhole-shaped wound in the side of his head.  He had amnesia and retained the wound upon his head. 
He takes the key and decides against using it for the time being, as he sees his connection to chojins as a part of his overall destiny, and swears that he will rejoin Mantaro's team. He sees the match-up ceremony on television, which allows him to realise that Ikemen Muscle has taken his place and where to go next.  Chaos resumes his place on stage and assumes again the Kinnikuman Great mask. 
They travel by taxi to where they think their next match is due to occur.  It is revealed Mantaro mistook the place of the arena, due to the time difference, and the two of them have to walk to their next match.  They enter the match dressed as a Japanese comedian known as "Hard Gay". 
In the Blue Corner, Master Carpenter makes the first attack against Chaos Avenir, which barely misses. 
After managing to deliver a blow, Master Carpenter hits Chaos with his Hammer Hand. Chaos is then forced to constantly evade many oncoming blows, until Mantaro Kinniku teaches Chaos to block with unusual methods. After so many blocked techniques, Master Carpenter attempts a Storm Through Norwegian Forests. 
Chaos hits Master Carpenter with a Palm Strike, followed by a Hard Hay-Maker.  Master Carpenter proceeds to tell Plastic Modelman to use his Diorama Sensation, and helps him to use the Steam Locomotive Model.  This allows him to achieve a Wooden Joint Hold.  He uses a Storm Prison Gate, by taking Chaos in a Sleeper Hold from Behind, while Plastic Modelman uses a Head Scissors from the front.  They then spin Chaos around and throw him into Mantaro, before they use their Resident Model to create a version of Abraham Lincoln. 
After a while Master Carpenter returns to the ring with a Prison Gate Hinge-Drop.  Chaos then counters a move by Master Carpenter, allowing Mantaro to make find some reprieve.  Master Carpenter takes Mantaro into a Brain-Buster, while the Lincoln Doll takes Chaos into a Brain-Buster, but the Muscle Brothers Nouveau manage to counter them.  They defeat the Lincoln model.  Master Carpenter squirts glue all over the canvas, before using his Possessed Brush to turn the ring into liquid and while Mantaro struggles to swim, the Hell's Carpenters turn into a submarine. 
(More to Come)
During the battle, Chaos Avenir discovers that Plamoman's submarine kit is of the same type with which he also plays.  Chaos creates a breathing apparatus, just as Plamoman - in submarine form - takes a sharp turn, and dives beneath the waves.  There was no power source included with the model kit, so Plamoman improvised with the top rope of the ring, and Chaos snaps the rope to stop the propeller, which - in turn - stops the ship from movement.  Mantaro Kinniku throws Master Carpenter down upon Plamoman in an attack, which harms him. 
The bridge of the U-boat cracks open, and Plamoman falls to pieces due to the attack. He then sucks all his pieces back to him, but is left with only the runner and none of the pieces in place.Chaos then catches Plamoman, and then prepares with Mantaro to use the Muscle Docking technique. 
They try to win with the Muscle Docking, but Chaos becomes too scared to complete it, forcing Mantaro to defeat Deiku Toryu with a Muscle G. With support from Mantaro, Rinko, Sister, and the others, he is finally able to defeat PlaMoman with a Power Bomb, earning a victory for the Muscle Brothers Nouveau. Afterwards, the four competitors become friends.
Chaos is later seen watching the Reserve Match between the Five Disasters and the Handblades. He reveals that he greatly admires Geronimo, both being humans who fought alongside the Justice Chojins. Chaos later trains alone in the rain, until Rinko arrives with his old friends from the Bogus Chojin Wrestling Show. Recently, Chaos was greatly surprised to learn that Mari Nikaido was Rinko's mother.
The Muscle Brothers Nouveau are currently fighting the 20 Million Powers in an Electric Cage Match. Because they are a newly formed team, they have yet to master the timing of their combo attacks and are soon overpowered by the 20 Million Powers. Recently, Chaos' memories have been restored and his aura tore apart the Great Mask and costume. He unleashed a series of attacks on Buffaloman proving he is more the he appears to be.
During the fight the 20 Million Powers used the Long horn train but, they countered also using the Long Horn Train using Chaos's legs as the horns. It caught the 20 Million Powers off guard then Chaos puts the Japanese leg roll on Mongolman, while Mantaro puts Buffaloman in the Muscle G making their new move the Muscle Evolution. The move defeats the duo and destroys the Mongol Mask.
Semi-Finals: First Round
Chaos enters the left-most ring in perfect sync with Mantaro. 
When Kinnikuman announces a mask versus mask match, Chaos agrees on seeing Mantaro agree, as he completely trusts Mantaro.  Chaos offers to go first in the ring, to protect Mantaro, but Mantaro strikes him and enters the ring first.  He stays on the side of the ring, where he is able to offer advice to Mantaro.  After a series of failed attempts to tag into the match, Chaos finally attempts to attack Terryman from behind.  Chaos is then sent reeling by a kick from Kinnikuman.
The two are thrown against one another, and then suffer drop-kicks to the back of the head, which sends them onto the canvas.  Chaos - inspired by Ramenman's spirit - attacks Terryman, and together with Mantaro, they are able to counter-attack against The Machineguns.  Together, they use the Man-Cha Drop.  Chaos manages to then inspire Mantaro, as they seemingly gain the upper-hand. 
After Kinnikuman rids himself of the Demon Hourglass, Chaos continues to offer support to Mantaro while he fights against Kinnikuman alone on the ring.  Chaos is horrified by Kinnikuman's action, such as trying to remove Mantaro's mask, as it goes against what he knows as a Justice Chojin.  Chaos is tagged into the match and saves Mantaro with a Guillotine Drop, and - as Terryman enters the ring - stops him with a Flying Knee Kick.  Chaos is then struck by The Machineguns' Cross Bomber. 
Despite his injury, Chaos stops them using the Cross Bomber on Mantaro. Terryman strikes Chaos with a Texas Condor Kick, before using the tag-team move of Building Demolition Drop, and Terryman strikes him over and over with a barrage of blows.  Chaos and Terryman exchange a series of blows, until Chaos is able to gain the upper-hand by striking Terryman with the corner-post and forcing him to switch with Kinnikuman.  The Machineguns strike Mantaro with a W-Kinniku Buster. 
Chaos then transcends to another plane of existence, where he meets the spirit of Ramenman.  Ramenman teaches him about Friendship Power and teamwork, while Rinko Nikaido encourages him in his favourite cosplay from outside of the ring, and he awakens and is sent hurtling into the glass, which breaks and cuts Rinko's leg.  Rinko inspires Chaos to switch with Mantaro. 
Chaos is tagged back into the ring and uses a Double-Shoulder Buster with Mantaro against The Machineguns.  They then use a Moonsault Head-Lock against Terryman.  The Machineguns attempt a Muscle Docking, but - due to Kinnikuman's error - it is not at full power.  A second Muscle Docking is attempted, but is countered by a Skull Campana.  In an exchange of blows, Kinnikuman and Mantaro are thrown from the war-cube and Chaos must help them stay in with Terryman. 
The match is fought evenly from that point forward, until a Muscle Docking is attempted again.  Mantaro uses his Fire of Inner Strength, and Chaos counters the attack with him, rendering it useless against them.  Chaos hits Terryman with a Skull Stapler, as Mantaro uses a Buster Crash on Kinnikuman, and together they use the Muscle Evolution.  The Machineguns and Muscle Brothers Nouveau are both knocked down, as a countdown begins to be counted.  Chaos and Mantaro stand.
They are declared the winners of the match. 
Rinko embraces Chaos, as he leaves the ring.  He sneaks away to confront Thunder and Lightning over the murder of his parents, and reveals his keyhole-shaped scar on the side of his head, as he explains his history to them and how he seeks to avenge his parents.  Chaos starts a fight with the Five Disasters, until Rinko and Mantaro come to his side and offer an excuse for his actions, and - holding hands with Rinko - Chaos returns to the Sister and orphans to celebrate. 
Semi-Finals: Second Round
Chaos later dies during this same arc. He is replaced by Kevin Mask in "Muscle Nouveau", who has made a full recovery, and Kevin fights initially in Chaos' "Great" mask, before he wins the final match in Chaos' honour. Chaos is buried in the grave seen at the start of the arc, in which only the stylised 'OS' remained. He can be seen in spirit several times, offering inspiration to those around him.
Chaos's future is so far unclear. 
During a time period known as the Justice Rest (正義の安息（ジャスティス・レスト）), many legends such as Kinnikuman, Terryman, and Robin Mask were raising their children, and others like Ramenman, Buffaloman, and Brocken Jr. were settling into retirement.  A wave of Brutal Chojin seized the opportunity and attacked Earth. In the Choujin Encyclopedia (超人大全, Choujin Taizen) this incident is referred to as the Rain of Brutality (残虐の雨, Zangyaku no Ame). They were defeated by a lone Justice Chojin.
The name of this chojin is unknown to Meat and Mantaro (due to Mantaro ripping the Encyclopedia page out and using it as toilet paper before Meat could read his name).  Mantaro is very sure that this man is Chaos, but Meat and Chaos himself are sceptical.  Furthermore, before the time-ship Kevin Mask can take off, Mantaro is sent out to remove a headstone that is blocking it's path.  The first letters in the name on the headstone are covered in dirt, but the last two letters are "ΘS". 
W Kinniku Buster
Chaos Sphere Bottom
King German Suplex
Muscle Docking (failed)
- Saviour of the Interval (間隙の救世主, Kangeki no Kyuuseishu)
- The Man who Creates Legends (伝説を作り出す男, Densetsu wo Tsukuridasu Otoko)
- Saviour of the Era (時代の救世主, Jidai no Kyuuseishu)
- Win/Loss Record (Singles)
- O Minutes Avenir (King German Suplex)
- O Itto Mask, Robin Mouse (W Kinniku Buster)
- Win/Loss Record (Tag)
- Kinnikuman Manias (Mantaro Kinniku)
- O Beefman, Curry Lou Thesz, Faux Lupin (Arm Hook Double Dropkick)
- O Tenmusuman (Double Brainbuster)
- O Itto Mask (Unnamed Combo Technique)
- Muscle Brothers Nouveau (Mantaro Kinniku)
- Δ Hell Expansions (Interference) (as Great III)
- O Hell Carpenters (Muscle Gravity) (as Great III)
- O 20 Million Powers (Muscle Evolution) (as Great III)
- O The Machineguns (Muscle Evolution)
- Submitted by: Megumi Kaneda (兼田恵) of Kanagawa and Ōshaku Yoshida (吉田大錫) of Osaka
- Least Favourite Food: Beni shoga
- Favourite Celebrity: Seiko Matsuda
- He refers to himself in the first person as Wachiki (ワチキ), occasionally using the more common Boku (ボク). He also refers to Sister as Mother (マザー).