Shikata Clan

The Shikata Clan (方谷族, Shikata Ichizoku) is a group of rogue shinigami that currently reside in the Human World. Originally a part of the Soul Society, the clan objected to the mass slaughter of the Quincy, along with other similar acts, and traveled to the World of the Living, where they established a small colony and began to perform Shinigami duties while not affiliated with the Soul Society. Shikata Clan shinigami are mostly noticeable due to their lack of any form of Shihakushō, with each individual member wearing what they prefer.

Due to their actions, the Soul Society entered a short-lived war with the clan, resulting in heavy casualties on both sides, as well as a series of rules imposed on the Clan that, as long as they were followed, would allow them to continue their business without interference from Soul Society.

Trivia

 * Their symbol is the second symbol of the Asakura Family from the anime/manga series Shaman King.