>Imperium of Man
Hololive, the current greatest empire, but falling into stagnation
>God-Emperor of Mankind
YAGOO, complete with the cult of personality
>Horus
Kiryu Coco/Kson, once one of the most favoured of the Idols (Primarchs) and the most overachieving, the Rising Star, the Legend of Legends, culminating in the HoloEN Crusade which conquered the Vtubing galaxy. Crowned by the Emperor as His successor on her graduation, even knelt to her. Fell and became the leader of the very thing seeking to destroy Hololive and everything it represents, which is...
>Chaos
Vshojo. Twitch is the Warp. Ironmouse is Nurgle for her sickliness, Melody is Slaanesh for being a literal pornstar (or Veibae to represent Excess and depravity at its worst), Nyanners is Tzeentch since she's canonically Nyarlathotep and also a backstabber nurtured by 4chan, I don't know about Khorne, maybe Zentreya
>Eldar
Nijisanji. The former great power of the Vtubing galaxy, but fell and superseded by the Imperium
>Orks
Indies for obvious reasons
>Necrons
Kizuna Ai, the AIs that preceded everything else before the rise of Niji and then Hololive. Went into hibernation.
>Tau
Phase Connect, though a small empire, is rising to become the most powerful and influential of the small/xeno corpos, able to go toe to toe with the lowest Nijis. Incorporated Xenos into its society (Lumi from Cyberlive) and in the process of absorbing other Xenos (Tsunderia). Pippa, Lumi and Yuri are the Farsight Enclaves. Still tiny compared to Hololive though
>Tyranids
Now this is someting that's more of an outside context problem. any ideas?

Other ideas: Lorgar is Rushia (personally rebuked by the Emperor, aka fired, and to some sources that was what made Coco/Horus turn to Vshojo), Erebus is Artia (the absolute Judas who manipulated all this heresy thing, seriously FUCK ARTIA!!!), Flare is Vulkan (black and also flare is a fire), Kanata is Sanguinius (Angel, and it would also be tragic if the Angel who loved the Arch-traitor the most got slain by the arch-traitor herself) either Suisei or Fubuki can be Guilliman, A-chan is Malcador (the power behind the throne). Feel free to add.