Seiji Noumi (能美 征二, Nōmi Seiji) is a student at Umesato Junior High School and is a member of the Kendo club. He is the main antagonist of the third and fourth arc of Accel World.
Upon his introduction, Seiji was an extremely twisted person, whose personality stemmed from the years of extreme bullying he received at the hands of his brother. He was a hardcore Burst Linker who constantly misused acceleration to ace everything, claiming it was because he "likes taking things". He was also utterly merciless, as shown by him even going as far as to blackmail other players and force them to work for him as slaves by giving him their points. In addition, due to his past where his only friend betrayed him under his older brother's influence, he has a very strong disdain towards bonds and friendship.
However, since losing Brain Burst, he has become very kind, pleasant and carefree. This likely stems from his loss of Brain Burst erasing his memories as a Burst Linker, including the memories of his immense emotional pain and abuse he has suffered at the hands of his brother.
Seiji had an extremely unhappy childhood as his brother, Yuichi Noumi, would forcefully take toys and money from him, even forcing his only friend to sever their friendship. At some point, Yuichi introduced Seiji introduced to Brain Burst. However, he then threatened him into fighting Duels and earn Burst Points for him. Any attempt to resist resulted in Seiji getting beat up in the real world. He would later describe his treatment as "slavery" and it eventually drove his sanity to the breaking point.
As time passed, Seiji gained more experience as a Burst Linker, slowly accumulating sufficient burst points to level up and strengthen his Duel Avatar; gaining his Demonic Commandeer ability. As his battle experience continued to grow, he eventually learned of the Incarnate System. He then tricked his older brother into the Unlimited Field, stole his Duel Avatar's ability and proceeded to use Incarnation to put him in Endless Kill Mode; a process where Seiji repeatly killed Yuichi until he lost all his points. At some point afterwards, he joined the Acceleration Research Society.
Seiji has a medium stature, dark brown hair which he has in a bowl haircut and brownish gray eyes. As for his attire, he has been seen in Umesato's school uniform which consists of a white dress shirt with a light blue blazer on top and a green tie.
Dusk Robber Arc
Seiji arrived as the first year at Umesato Junior High School. He was later revealed as a Burst Linker when he soundly bested Takumu Mayuzumi in a kendo match. Taku theorized that Seiji used Physical Burst, which allows a Burst Linker to accelerate for three seconds at the cost of five Burst Points.
Taku tried to confirm whether Seiji was a burst linker by trying to connect to his Neuro Linker but failed to do so, he sent Haru a picture of a graduate of Umesato Junior High School from 3 years ago who he believed to be Seiji Noumi's Elder Brother, unknown to Taku and Haru at the time, the picture contained a visual masking virus that was installed into Haru's Neuro Linker. Haru began to tail Seiji the next day but the latter was on to him and lured him into the girls' shower due to the visual masking virus in Haru's Neuro Linker mixing up the gender signs on the wall. The next day, he arranged a meeting with Haru, revealing that he had secretly placed cameras recording Haru entering the girls' shower. He then began to blackmail Haru, demanding that he give Burst Points every day if he doesn't want to be expelled. Chiyuri Kurashima then arrived, trying to cover for Haru, only for Seiji to reveal one of the cameras to the school. He then grabbed Chiyu, telling her to cooperate and root for him as he attempted a direct link with her. Haru then charged at him and they both used Physical Burst. But as this was Haru's first time using the command, he was beaten. Seiji then pinned the boy to the ground with his foot and direct linked with him as he challenged him to a match. He defeats him after using his special ability, "Demonic Commandeer" to steal Haruyuki's ability to fly and rendering him powerless. He promised to return Haru's wings when he graduates, on the condition that he gives Burst Points to him every day. The next day, as Seiji was taking a test, he was challenged to a match by Taku, who knew he would accelerate during the test and that he stole Haru's wings. Even at a disadvantage with his stolen abilities in the match until then.
Seiji then demonstrated the power of the Incarnation System, enabling him to best Taku. Haru manages to trick Seiji into switching to Battle Royale mode so he can fight against him instead, managing to cut off one of his arms with his own incarnation attack. As Seiji activates Haru's wings and some pyro equipment, Haru equips the Gale Thruster he received from Sky Raker, allowing him to take to the skies and face him head-on and manages to beat him with assistance from Takumu. However, before Haru can finish him, Chiyuri/Lime Bell appears and heals Seiji.
Afterwards, Seiji flaunts his ownership over Haru's wings and Lime Bell's healing ability. This causes Haru to attack Seiji, but he is pushed back as Taku advances forward. Seiji quickly uses the Incarnate system to tear Taku to shreds, causing Chiyu to scream and Haru to become even angrier. In his anger, the Chrome Disaster armor that attached on Haru begins to entice Haru into brutally destroying Seiji. Haru eventually succumbs to the temptation and uses a darker version of his incarnate system to attack Seiji, screaming at Seiji to get out of his life and disappear. Eventually, Seiji has to use both hands powered by his incarnate system to hold Haru off, but just as Haru was getting the upperhand, the match timed out, causing all the players to go back to the real world.
Flight Towards the Blue Sky Arc
Seiji soon leaked a rumor that Haru planted the camera in the girls' shower room, which led to him being questioned by a staff member and unjustly beaten up by a fellow student whose girlfriend was embarrassed by the revelation. Seiji stared at Haru in triumph as his rival ate his lunch without crying.
Over the next little while, Seiji, with Chiyu by his side, began to dominate the Suginami area, devastating entire opponents in the normal matches. It was his ambition to eventually become powerful enough to challenge Black Lotus and rule Suginami.
A few days later, Haru confronts Seiji in the same bush where he first challenged him. He reveals that he knows he's using an illegal brain implant chip to hide from the matching list and to cheat on school exams, only activating his Neuro Linker to challenge people, to Seiji's surprise. One scan and Seiji would be expelled, his implant chip forever deactivated.
Seeing that he knows his secret, Seiji offers a chance to end their feud once and for all by wagering all their Burst Points in the Unlimited Field in a Sudden Death Match.
However, Seiji was not seeking to fight fair. He enlisted the assistance of Black Vise, vice president of the Acceleration Research Society, to trap Haru while he engaged Taku. However, Taku revealed to mastered the incarnate system, turning his pile driver into a sword. They then dueled, eventually slashing off Seiji's left arm. Taku then observed that from his duel avatar's name, he can never truly own the things he steals, which is why he's left with nothing. Seiji simply laughed, revealing how came to possess Brain Burst and avenged himself upon his bullying older brother. He then manifested a new arm, which he used to constrict Chiyu and torture her, causing Taku to lose his will to fight. Seiji then proceeded to viciously attack Taku. His sadistic attack soon gave Haru the strength to break free of Vice's grip. But before Seiji could land the killing blow to Taku, his right arm is severed by Black Lotus, whose duel avatar had journeyed all the way from Okinawa. She held off Black Vise while Haru faced Dusk Taker for what may be the last time.
Seiji merely laughed at Haru and the thought that their bond of friendship could defeat him, promising to take his time with him just like he did his brother. Haru told him that his biggest mistake was not challenging normally him when they first met. If he had, Seiji would've gained what he wanted most: friendship. However, he is not seeking to befriend him, seeing that Seiji is beyond redemption. Silver Crow and Dusk Taker then engaged in an aerial battle. When it seemed like Haru was going to win, Chiyu suddenly used her healing ability on Seiji. The tide had turned and Seiji had Haru in his grasp. Then suddenly, his wings disappeared and were returned to Haru. As Seiji went into freefall, Haru used the combination of his wings, Laser Sword and Gale Thruster to deliver a crushing blow to his opponent. By then, all what remained of Dusk Taker was his upper torso, head and left tentacles. Chiyu reveals to Seiji that she's come to the revelation that her healing ability, in fact, reversing time on duel avatars, given that his equipment regenerated the first time she healed him. Thus, she pretended to join him long enough to level up her killer move to the point where it could reverse time to before Haru lost his wings.
Cursing the Nega Nebulous, Seiji vowed to leak their real identities and called on Black Vise to help him. Unfortunately, Black Vise was tied up holding off Black Lotus. Seiji demanded that he do something, threatening to expose the Research Group and the BIC. Black Vise reveals that the BIC will dissolve into the cerebrospinal fluid once it senses Brain Burst's uninstalling. He then vanished into the shadows.
Left with no allies, Seiji started pleading for his life. He attempted to bargain points and his service in their legion if they spare him, but his pleas fell on deaf ears. Growing frantic, Seiji tried crawling away, only to be sliced in half by Haru. Dusk Taker was then destroyed, once and for all.
The next day, Haru met Seiji at school, now a much more pleasant person without Brain Burst, though he could not recall the game.
Dusk Taker has a tall black and purple body with a red orb as his face. There are two similar orbs on each of his shoulders. His left hand is normally equipped with an Enhanced Armament that takes the form of triage of tentacles with the power to regenerate, which he apparently stole from another burst linker called "Starfish". His other hand is equipped with another Enhanced Armament that looks like a giant metal claw that has extremely strong cutting power, and which he sometimes exchanges with for a large red flamethrower-esque cannon known as Pyro Dealer which is capable of firing great blasts of flames like a dragon, that can burn the stage's ground into lava. However, it was not stated who he stole either of these weapons from. Dusk Taker also gained a pair of torn wings which resemble that of a bat or demon that he stole from Haruyuki's Duel Avatar, Silver Crow. His avatar is focused on speed, much like Silver Crow, and was fast enough to match him.
Dusk Taker is a unique duel avatar due to its ability to steal the abilities of other Burst Linkers, and due to his past where he was forced to regularly give Burst Points to his older brother, Taker spent an enormous amount of battle time in the Accelerated World, thus he has immense combat experience as a Burst Linker when compared to other Burst Linker beginners such as Cyan Pile and Silver Crow, despite his level being lower than the other Six Kings and their close aides, he has superior tactical prowess and versatile mastery of the Incarnate System. This makes him an exceedingly strong Burst Linker when combined with his arsenal of Enhanced Armaments and special abilities which he stole from others.
- Pyro Dealer – Stolen from an unnamed Burst Linker. When equipped his arm turns into a red and black cannon that fires magma-like fire.
- Unnamed metal claw – Stolen from an unnamed Burst Linker. This Enhanced Armament is mounted on the back of his right arm, and looks like weaponized bolt cutters.
- Unnamed tentacles – Stolen from an unnamed Burst Linker. This Enhanced Armament is a group of three tentacles that regenerate, and can be used to bind opponents. Their previous owner claims they are part of a starfish, although Dusk Taker's version may differ due to the different aesthetic taken on by stolen objects.
- Demonic Commandeer – Dusk Taker's only native non-Incarnate ability, a Special Move born from Seiji's extremely painful trauma of his dark past where he suffered extremely cruel emotional abuse by his older brother, it allows him to steal an opponent's Special Moves, Enhanced Armaments, or Abilities. Once Dusk Taker has taken one of these 3 things, he can use them however he wants. He can swap out whatever he steals at any time and keep them for as long as he so chooses. He can also give anything he steals back to the Burst Linker he stole it from, but this is very unlikely. According to Dusk Taker himself, there is a limit on how many he can hold such as abilities, armaments and such that he can steal, but the exact number is not revealed. However, this ability is not foolproof. Dusk Taker is unable to steal abilities or Armaments from opponents which have been crafted from very dark or vicious traumas or memories, as shown when he is unsuccessful in stealing Cyan Pile's Cyan Blade and explaining why he did not attempt to steal Lime Bell's healing ability, as both are deeply forged from their owners various traumas. Stolen abilities or Enhanced Armaments will change shape and even attributes to suit Dusk Taker better.
- Aviation (formerly) – Stolen from Silver Crow. His two wings look like a bat's, different from Silver Crow's ten blades (light novel) or two hexagon-tiled sheets (anime). It has since been returned to Silver Crow by Lime Bell's Citron Call Mode II.
- Nihilistic Fluctuations – A general name by Silver Crow and Cyan Pile for Dusk Taker's negative Incarnation, likely an attack power-enhancing skill. It has been seen taking the form of scythe-like claws and a blade. The claws grant him enough strength to throw around the bulky and heavily armored Cyan Pile as well as overpower his older brother's massive Duel Avatar; The blade is strong enough to clash with Cyan Pile's Cyan Blade. The use of Incarnation, along with his speed, makes him a very dangerous opponent.
- Taker stole two other Linker's abilities who probably were bullied by someone like he was.