Given the overall attention to detail, I tried to figure out the uniforms in the anime, but they seem to be rather mix and match. For some reason, everyone has red trim on their uniform. The color of the trim in the German Empire was regional until it became a branch indicator in 1921 (Waffenfarbe). Red trim was for artillery under the Reichsheer (and also for generals) which might fit for assault mages, but we see the same on infantry (which should have white trim), or everyone else really,
The ranks at least seem to be consistent. When they first met, Rerugen was a Major, while Tanya’s shoulderboards have the wide trim of a noncommisioned officer (Unteroffizier), with 3 pips (Stabsfeldwebel, probably equivalent to staff sergeant or sergeant-major).
The animators seem to misunderstand or not care about the two cockades on all imperial headgear – the top one for the Empire, the bottom one for the regional monarchies composing the Empire – since they are always rendered as identical featureless discs.
As Leutnant, Tanya is entitled to wear a sword (with Portepee), though she never does so again after this one scene (I speculate that she realized her arms are too short to actually draw it).
Note that the army has already switched from embroidered collars to sewn-on Kragenspiegels:
Oberleutnant is one pip above Leutnant:
Tanya promoted to Oberleutnant while in school:
Tanya promoted to Major:
Oberstleutnant is one pip above Major.
For some unexplained reason, the 203 Batallion wears the Ulan (lancer) uniform, but fortunately without the silly hats:
Silly Ulan hats:
Everyone (including Tanya, somewhat redundantly) received an iron cross second class after halting the Dacian invasion between episode 5:
and episode 6, as indicated by the ribbons worn in their second tunic button: