Seidou Gōitsu is both an advanced and dangerous technique part of the Ancient Martial Arts Isshinsai Ogata made by combining the opposing Ki of Sei and Dou. Seidou Gōitsu works by having first ki being focused inward, while second ki explode outward resulting in an explosive boost in the user's physical abilities and techniques.
According to Isshinsai Ogata, this technique can only be taught to a small number of fighters who have a natural ability to use both ki of Sei and Dou. Ryūto Asamiya, Shō Kanō, and Rimi Kokorone all learned this technique. Although Kenichi has the potential to learn and use this technique.
Ogata noted that in order to use this technique without devastating side-effects, the user must keep their emotions under tight control, which neither Ryūto or Rimi could accomplish. Although, Shō has proven to be able to use Seidou Gōitsu effectively against Kenichi even breaking through his Ryūsui Seikūken likely due to all of his training from childhood in isolation. Shō himself elaborated that the secret of using Seidou Gōitsu was to compress ki, then after being ignited release it all at once.
After pretending to be crippled to realign his ki, Ryūto was able to gain control over this technique and use it for 30 seconds without any physical side effects. Recently, after a long absence, he used the Seidou Gōitsu against Sōgaku Chin, a Master Weapon User. However, it is unknown if Ryūto perfected it or not.
Isshinsai Ogata, the creator of Seidou Gōitsu finally showed it in the final battle against the Ryōzanpaku Grand Masters, Shio Sakaki, Akisame Kōetsuji, Apachai Hopachai, and Kensei Ma; allied with Cyril Rahman, Agaard Jum Sai and Sōgetsu Ma during the Eternal Sunset Arc. He was able to defeat Cyril Rahman, who described the technique to be evil.
Due to the powerful fusion of both Sei and Do Ki types, Seidou Gōitsu can level up the user beyond their normal level of skill and power. This is first shown as Ryūto and Rimi, two High Class Disciple achieved a power almost comparable to that of an Expert. Using Seidou Gōitsu, this granted Isshinsai Ogata power that brought him to the level Advanced Grand Master, possibly even close to the level of a Legendary Master. This increase of power enabled Ogata to defeat two Grand Master, Rahman and Agaard, who are considered powerhouses in the martial art world within seconds, one after another. An impressive feat in this series, as Agaard's fighting prowess, has been fully portrayed many times and it's consistently on par with the skills of other Grandmasters.
However, due to the conflicting nature of the Sei and Dou ki, excessive use of Seidou Gōitsu caused a disruption in one's flow of ki resulting in crippling, even fatal damage to the user. Ryūto had experienced tremendous stress after using Seidou Gōitsu, to the point where both his hair turned white and one of his sclera turned black and he was bound in a wheelchair due to his legs being too damaged to support him. Although, it was later revealed that Ryūto was thinking about how to balance and control his ki.
- Seidou Gōitsu has various similarities to Satsui no Hado from the Street Fighters series.