Seimei is an anime-only character of the Naruto anime and the title antagonist of the final pre-Shippuden filler arc, the Seimei Revival Arc. He was the founder of the Village of Artisans and its greatest shinobi.
Seimei was born at an undetermined point in the past and during the course of his life founded his own village, naming it the Village of Artisans, which went on the be famous for making some of the greatest shinobi weapons throughout the Five Great Nations. He died 100 years before the time of the Seimei Revival Arc in the anime, having been his village's greatest shinobi and considered its ultimate ninja tool.
Revival, failed attempt at Conquest, and DeathHoping to be able to conquer the other shinobi lands in doing so, Hoki, a shinobi of Seimei's village, and his team, the Four Celestials, plotted to revive him by using the chakra of Shukaku, Gaara's Tailed Beast, which Hoki himself successfully used together with sacrificing his own body to do so. Activating the armor and weapon suit Hoki himself had used, Seimei introduced himself, stating he'd been revived as his village's ultimate ninja tool. Easily overpowering Naruto Uzumaki while continuously absorbing Shukaku's chakra out of Gaara, Seimei expressed delight at being able to face the Tailed Beast after Gaara, partially transformed into him, broke out of his cage. However, Gaara forced the transfromation off, with Seimei proceeding to arrogantly mock him and injure him with his swords(Gaara's Ultimate Defense had been drained of chakra at this point). However, the jinchuriki fought back by using the surrounding rock to create a tidal wave of sand which burried Seimei alive. Emerging surprised at how much chakra Gaara had left, Seimei attempted to steal what remained, only to have his armor weapon destroyed when Gaara threw a mineral-enhanced spear at him. In utter disbelief, Seimei was then promptly burried alive and crushed to death by Gaara's Giant Sand Burial jutsu.
Seimei, as the founder of the Village of Artisans, was extremely loyal to it and took his responsibility as leader very seriously. He was also extremely arrogant towards his enemies, believing their efforts against him to be in vain, and openly mocked them. He also believed shinobi were just fighting tools.