Seito

was once a member of the Twelve Guardian Ninja.

Background
While he was still alive he was part of the Twelve Guardian Ninja. Ten years before the start of the series, six of the members tried a coup d'etat. He, alongside Asuma Sarutobi, Chiriku, Kitane, Tōu, and Nauma fought against them, only to be killed by Kazuma when Seito and the three other survivors tried to use Limelight on him.

Abilities
He had an elemental affinity for lightning. When in the the four cardinal directions he, Kitane, Tōu, and Nauma could use a jutsu called Limelight to reduce everything within the area they had surrounded to ash.

Twelve Guardian Ninja Arc
During the beginning of the filler arc his, along with Kitane's, Tōu's, and Nauma's corpses were stolen by grave robbers, and they were later revived using lightning. After being revived they were all approached by Asuma, who had figured out the scheme of the robbers. There he tried, without success, to stop the three of them, who seemed to have become mindless puppets. He started walking towards an unknown point whilst emitting large amounts of lightning, and, after arriving at his destination, began preparing his part of the Limelight technique. When Kitane was killed by Asuma Sarutobi, Kazuma's plan failed, and he decided to release the summoned Nauma, Tōu, and Seito.