I adore the vostroyan and their whole asthetic
They are a regiment of the imperial guard coming from the Industrial planet of Vostroya, they joined the guard to correct their planet's past dishonour, Vostroya once declined sending their people to the guard because of how difficult it was to keep up with the industrial production, as a way to atone with that, they made a deal with the imperium, the firstborn of every single family of Vostroya is sent to the guard
Their equipment looks high quality and ornate mostly because its handmade in their own planet, a lot of times by their own family members
Most of their asthetic is inspired by the real world Slavic cossacks, their hats are just really exaggerated ushankas
Their uniform is not only a reference to the real cossacks but also a reference to the adeptus mechanicus of mars, a faction that is really close to the Vostroyans since Vostroya is an industrial world
I also like how their masks look steampunk