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.

Fire Temple arc
During the beginning of the filler arc is his, Kitane's, Tōu's, and Nauma's corpses are stolen by grave robbers, and later revived using lightning. After being revived they were all approached by Asuma who had figured out the scheme of the robbers. There he tries without luck to stop the three who seem to have become mindless puppets. He started walking towards an unknown point emitting large amounts of lightning, only to arrive and prepare 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.

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