The Fumeiyuna are a group of shinigami that had been betrayed by the Gotei 13 and have gone into hiding. They are mainly made out of Captains, Lieutenants and seated officers.
The Fumeiyuna was originally various shinigami that were involved with operations in the Seireitei Hollow Dispute. Oheina Buruto, Chimamire Shinko, Ochitsuki Yoru, Tsukereta Noburu and Sekkachi Shubo-Sha were in a convoy taking Lady Shubo-Sha to a safehouse outside of Seireitei.
Chishi Gomon, Yajiri Hokuai, Kurai Kudoku and Umi Jonetsu were in an investigation squad looking into the disappearance of Isamu and Hiroto from Squad 3 300 years ago.
A high-ranking member plotted for an ambush, using the convoy as bait, and the investigation team as the location. Explosives were set and went off successfully, but unknown to the Gotei 13 they survived. The newly founded Fumeiyuna escaped and set their plans to action.