A combat method that involves controlling the entire radius within one's arm length, creating a spherical shield around oneself. It can be used for offence and defence. Weapon users such as Kagerō Kii can extend the range to several feet around them with the additional length of their weapons, allowing them to defend even at mid-range. More experienced fighters can even extend the range with minimal lengths by using air pressure. However, a Seikūken with a larger radius is not necessarily better, as Odin had his jacket grabbed by Kenichi when one of his arms were brushed aside, leaving him open at extremely close range. Besides having a larger radius, having a Seikūken with a very small radius can also be useful too.
The Seikūken can only be erected with a calm mind (i.e. jumping around or moving will make it difficult). if one is not calm, it would be near impossible for him or her to erect the Seikūken. In volume 16 of the manga, during his battle with Kenichi, Odin shows that he is able to overcome this limitation by making Seikūken an instinctive reaction.
Odin supplements this technique by releasing high amounts of ki, allowing him to confuse and scare his opponents, causing wayward attacks. The Sei type masters at Ryōzanpaku were able to implement Seikūken with just their mind, implying that this technique is a foundation or is at least the basic form of many combat techniques. In Battle 179, Boris Ivanov shows that the Seikūken, or at least, Kenichi's, leaves the legs defenseless, as the technique mainly involves the use of the upper body, though this could be countered if the user sits down. It is also not well suited against combination attacks since its defencive function is to deflect incoming attacks. The next level is Ryūsui Seikūken which has more power then Seikūken.
Having a Seikūken with a very small radius can also be useful too. The best example of this is shown when Shōgo creates a smaller and stronger Seikūken by keeping his hands tucked in his pockets. Kenichi noted that this was a ingenious move because it makes him able to attack while at the same time using the small Seikūken to defend. This is best at close-range combat, and was able to crush Kenichi's own Seikūken.