Seitarō Raigō is the Kodachi user of the Hachiou Executioner Blade and is a member of the Yami Armed Division.
He is a very tall and muscular man with long black hair in a ponytail in the back. He wears dark sunglasses and a dark lether suit. He's seen with a sword on his hips.
He's a very serious man, as he takes his job very seriously. He's also perceptive, noting that Ryozanpaku caged Diego and Alexander in Big Lock using their pride as Martial Artists. His disciples note that he's a very strict person. He's also very respectable, greeting the masters of Yami with great respect. He is willing to take the Elder of the Ryouzanpaku to the Inland to fight Ganosuke Yokiou.
- Master Swordsman: As a member of the Hachiou Executioner Blade, Seitaro is a highly-skilled weapons user that specializes in swordplay. His weapon of choice is the kodachi (short sword) which he has mastered to a degree where he can perform multiple slashes at very high speeds. His main skills with the kodachi seem to be slashing and stabbing attacks, and when combined with his speed, Seitaro can be a dangerous opponent. His mastery of Kenjutsu is so great that he can perform Shinto Kourenzan, which is known as the highest level of sword mastery. He managed to hold his own against the Elder, while luring him to to the island to fight Ganosuke Yokio and only received a light shoulder injury during their clash.
- Immense Speed and Reflexes: Seitaro has displayed incredible speed, as seen when he was able to avoid setting of multiple land mines hidden in the snowfield on Big Lock. A true testimate to his skills is his ability to run on water, a feat only previously displayed by the Elder and Mikumo. Likewise his reflexes are on par with his speed, as seen when managed to avoid multiple strikes from the Invincible Superman himself.
- Master Infiltrator: Aside from his martial and weapon skills, Seitaro has displayed master-level skill in infiltration. His skills are great enough to be chosen by the One Shadow himself to infiltrate Big Lock to give a message to Alexander Gaidar and Diego Carlo about the return of the Hachiou Executioner Blade team. He displayed an inventive plan by using snowballs to trigger the laser defences and creating a smokescreen to conceal himself and running in zig-zags to avoid the minefields. He also displayed good disguise skills, though not enough to fool the Elder.
- Unique Ki: According to Mikumo Kushinada, despite being a Satsujinken follower, Seitaro's Ki has a similar quality to a Katsujinken user's, because of this he is well versed in the fighting style of Katsujinken and can easily copy and learn the techniques of the Katsujinken, as seen when he was able to perform the "Infinity" combo attack with Kushinada, despite it being a move only Katsujinken users can properly perform.
Seitarō was one of the members of the Yami Weapon Division who set out to retrieve the Akabanetou swords. He along with another Yami member went to retrieve two swords where they were confronted by the Hayato Furinji. During the fight he was able to take his unconscious partner and escape much to Hayato Furinji surprise.
Following the fight with Ogata and Tanaka, Seitarō was seen leaving the main base of Yami's with two of his disciples past Ogata
He is next seen with his two disciples arriving at Big Lock. After get past the security and making his way in side, he goes to visit the two One Shadow, Nine Fists members that are currently imprisoned in there, Alexander Gaidar and Diego Carlo and comments on how it must be difficult for them to escape. It is then revealed that they could easily escape anytime they want, and that they are willingly staying there because they lost to Ryozanpaku, and because they lost they must listen to the winners. They also commented on how they will escape only when there is a good enough reason for them to, to which he tells them both that the Hachiou Executioner Blade team is gathering again, asking them if that was a good enough reason before telling them the One Shadow sent him to tell them this. After leaving, he notes that Ryozanpaku imprisoned them using there pride as martial artists, which surprises him. Afterwards, one of his disciples ask if they should free some of the weapon masters imprisoned in Big Lock because they could be useful, to which he stated that they would be useful if they can escape on their own.
Later, he disguises himself as a boat captain with the elder on board, but his disguise is not enough to fool him and attacks him. The boat captain dodges and reveals a mask he was wearing and Hayato recognizes him as the Yami Kodachi user. When he asks if he was leading him into a trap, the Kodachi user flees as Hayato refuses to let him escape again and chases him on the water. He sees he's leading him to the island and accepts his chalenge and sends him crashing down. They clash and Hayato manages to land a wound on the Kodachi user and Hayato asks his name and the man introduces himself as Seitarō Raigō. When Hayato asks what good bringing him to this island does him, to which Seitaro states Ryozanpaku has a "mental cage" for locking the One Shadow Nine Fists at Big Lock and they have devised a counter with a "fighting cage". Just then, Hayato senses a very large ki that feels like it's going to swallow the whole island and that though there's an eery calm to it and feels as if it's the ki of nature. When Seitarō states his job was just to lure him to the island and that "he" will take over now, to which Hayato turns around and is shocked to see it's the leader of the Hachiou Executioner Blade: Ganosuke Yokiō and faces off against the weapon's master to which Seitarō states it is now checkmate.
One week later, while Yokio and the elder continue to fight, Seitaro greets the masters of Yami. When Agaard comments they don't have Yokio with them Seitaro says it was worth it stating they have the advantage in numbers and prepare to head out for the Eternal Sun.
He was later seen on the boat iwth the rest of the Hachio Executioner Blade members as Michael Schtilvay prepared to fight Shigure. However, Shigure instead takes on all seven, prompting Seitaro to scold her for doing something to recklace. As Michael stops Miu and Kenichi from escaping, Seitaro comments on how important this day is and how the cargo on the boat cannot be interfered no matter what. He then reveals the black flag of Yami so that the world can witness the Eternal Sun. As Shigure cuts open one of the containers revealing gold, Seitaro states there are 2000 tons of gold bars and is their military fund.
As Shigure continues to fight the Bow Master and Michael holds Kenichi and Miu hostage, Kenichi makes an opening by dancing oddly, prompting Seitaro to smirk asking if Michael is going to let them escape. He then reacts surprised at the arrival of Christopher Eclair and Mycroft saving the disciples. Seitaro then comments on how they didn't order for backup as he realizes the two masters are now against them. Before they fight, Seitaro asks the terms of the government's request and Christopher replies that they were simply told to "stop you people" as he engages with Christopher. Christopher gains an advantage as Savate is suited to fighting on bad terrain, such as on a boat. Christopher manages to trap him using his Tornado Over Kick and comments on him lacking a weapon despite being from the weapon division. Christopher notices Seitaro's kodachi and notices that he has been slashed, and Seitaro comments that he subconsciously protected a vital spot. Once Shigure uses her Soutou Kyourenzan, Seitaro fights his 'shadow' and allows her disciples to escape with Christopher and Mycroft.After Shigure's capture, Seitaro asks to make sure that she has no means of escape, stating that chains or even a piece of cloth can become a
Once the fighting across the world was taken cared of, Seitaro returns to base to hear of Shigure's escape, prompting him to agree with Michael stating the security is terrible. He tells the others to set out and find her in the base. Once the Eternal Sunset was starting, he was seen along side Saiga as he asked if it was the proper time, to which Saiga agreed it was to start the Third World War.
He then arrives on the battlefield where the Yami forces are fighting Ryozanpaku, to which he delivers a fatal blow to Sai. Apachai charges at Mikumo but is blocked and gets slashed by Raigou across the chest. The other Ryozanpaku masters jump in to help with their combination attack but are stopped by a combination from Mikumo and Raigou. Akisame wonders if the Satsujinken have managed to work together but Mikumo says that Raigou is familiar with Katsujinken techniques and thus was able to synchronize with Mikumo.
Deciding that it would be better if she went to the other battle herself, Mikumo seeks to end the battle against the Ryozanpaku masters. She causes an opening for the armed division to land a fatal blow on each of the masters but Akisame unleashes his true strength and manages to catch all the weapons before they land. However Seitaro Raigou appears behind Mikumo and aims to stab Akisame, who is unable to dodge the attack.
Kagero Sai regains consciousness and blocks the kodachi with his hoe and lands a punch on Raigou as well which destroys his sunglasses as well. After witnessing Agaard, Cyril and Sougetsu ally with Ryozanpaku, Seitaro agrees with Mikumo to progress the plan further.
The Ryozanpaku masters, along with Cyril Rahman, Ma Sougetsu, and Agaard are seen to have many injuries throughout their bodies as they face down Mikumo's group, with Mikumo's aura bearing down on them.
Mikumo unleashes her technique (Kushinada Style: Thousand-Year Throw) as she slams the ground with her hand, causing many hands made from her aura to sprout from the ground. Cyril warns to not touch the hands as they will result in instant death. The members of the Hachiou Executioner Blade take up their stances and utilize Shinto Kourenzan, and Kensei activates Seidou Goui. Once Agaard, Cyril and Sougetsu are defeated, Seitaro, Mikumo and Ogata face off against the Ryozanpaku masters in a heated fight.
Once Yami loses the battle, Raigo retreats with everyone else in complete defeat.
- Vs Hayato Fūrinji (undecided)
- Vs Hayato Furinji Round 2 (undecided)
- Vs Christopher Eclair (undecided)
- With Hachiou Executioner Blade (except Ganosuke and Michael), Mikumo Kushinada, and Ogata Isshinsai vs Ryozanpaku (except Hayato and Shigure), Cyril Rahman, Ma Sougetsu, and Agaard Jum Sai (Lost)
His appearance (specially his pony tail) resembles to the real life actor Steven Seagal when he was young.
While the manga never stated it, he appears to be the sub-leader of the the Hachiou Executioner Blade, as he was seen giving orders to the other members alongside Senzui and the members seem to respect him.
For the longest time, he was referred to as the "Wakizashi user" since when he made his debut prior to the last arc, his name was not revealed and the HSDK fan community simply referred to him as the "Wakizashi user"