With Shinryu's return, a report on the infomation he learned in Hueco Mundo has been delivered and dished out to all the Shinigami.
5 years ago Hueco Mundo was ruled by Ashlei Clixx, who was mostly absent, and Rose Mischevang (her sister). Ashlei was a Throne in Shadow Fall and one of it's leaders while Rose led the Shadow Espada (technically/kinda) in Shadow Fall. At the time, Nagato Tengan was still an Infante in SF (which are kinda like the equivalents of Seireitei's Noble Houses in terms of authority and power). Years prior the strongest Arrancar alive had been Nagato Tengan, Zefonse Kaizme, and Ashlei Clixx; by this point Zefonse was gone and Ashlei was mostly afk, leaving a pretty significant void in their wake. Eventually Ashlei went AWOL entirely and Nagato moved up to become a Shadow Fall throne and leader of Hueco Mundo. However he was never one to share power, and left Shadow Fall. This resulted in the newer power of Rose Mischevang becoming the new SF head honcho in Hueco Mundo. Nagato ended up creating his own faction, the Hollow Empire, and basically became a bordering/competing nation in HM to Shadow Fall. The empire grew and grew and grew....then stopped. Nagato disappeared like Aang the Avatar, his faction split and became leaderless, and Shadow Fall/Rose remained unimpeded in Hueco Mundo for a solid 2 years. Not much occurred there during this time. Random people came and went, and the Shadow Espada became barren with basically only Rose at it's helm and nobody else around.