Kasumiōji Clan

The Kasumiōji Clan is a wealthy family of Shinigami 'nobles' and are the main villains in the anime-exclusive Amagai arc. They have a loyal army of assassins that serve as their bodyguards and are led by Captain Hanza Nukui and (after the former's death) 3rd Seat Makoto Kifune of the Third Division. Their corrupt leader, Gyōkaku Kumoi, who had risen through the ranks by secretly assassinated several Kasumiōji Nobles/Family Members, secretly produces an illegal Zanpakutō-like weapon known as the Bakkōtō and wants to take control of the Soul Society by taking over all of it's noble families and subsequently eradicating the Shinigami to maintain his power among everyone else in the Soul Society. As of episode 187, the Kasumiōji Clan has already lost a large amount of nobles due to Kumoi's desperate actions, the Bakkōtō factory and Kumoi's illegal actions have been discovered by both the Ryoka and the Shinigami, the Kasumiōji Compound has already been leveled by the Gotei 13, the secret Bakkōtō factory was taken care of by Captain Soifon of the Second Division, Captains Hanza and Kifune have been killed by Ichigo Kurosaki and Izuru Kira respectively, and Kumoi himself was slain by Captain Amagai, the true villain of the arc.

Known Kasumiōji Nobles/Family Members
Princess Rurichiyo Kasumiōji - The true heir to the Kasumiōji throne.

Shū Kannogi - Rurichiyo's fiancé.

Gyōkaku Kumoi - The corrupt leader of the Kasumiōji Noble Family, the producer of the Bakkōtō, the one of the lead antagonists of the Amagai arc, and one of the two catalysts of The Kasumiōji Crisis.

Kasumiōji Associates
Captain Hanza Nukui - The leader of the Kasumiōji Assassins, Ichigo's first Kasumiōji rival, and the main antagonist during the first half of the Captain Amagai arc.

3rd Seat/Captain Makoto Kifune - Hanza's replacement, Third Division Lieutenant Izuru Kira's rival, Kumoi's unofficial 'apprentice', and the main antagonist during the second half of the Captain Amagai arc.

Captain Shūsuke Amagai - Captain Gin Ichimaru's replacement, temporary leader of the Third Division, and the lead antagonist of the Amagai arc.