It always struck me weird how vicious Tanya was in battle when most of the time, she's almost stoic except when it came to her career. But then I remember, Tanya's previous self stated that she was apathetic and had a lot of mental complexes that would fit with ASPD and the only thing that was leashing her was the rules of society. In the battlefield, where such rules get thrown out, her restrained nature, added with the fact she has to pray in order to use her Super Prototype computation jewel which pisses her off even more, and you get The Devil of the Rhine that is Tanya.
It's worth mentioning that World War I was notable as the first "industrial" war. Tanya was the pinnacle of industrial efficiency, so simply turned it to the prosecution of the war.
At first, Los!Los!Los! sounds like what a patrioticwar maniac would sing, with verses of how they seek the blood and gore of the battlefield and their enemies. That is until the last line of the song. "With an explosive sound that can even drown out their lingering hatred". This is the realization that Tanya's brutal tactics are for one reason only: To decimate their enemies so much that the Cycle of Revenge can't continue, because as she says in episode 12, people are so influenced by their emotions that they refuse to listen to reason and logic, that their desires for such must be quashed entirely. The fact that this line is said in a tired manner shows that Tanya likes war just as much as any other sane person does, which is not very much.
Tanya is very loosely following the career of Rommel. An energetic and demanding 2nd Lieutenant experience early success against an unprepared enemy the early French/Dacia she then is wounded and goes for more schooling returning to a different front with an elite unit. After success with the elite unit, she takes a strategic role (although Tanya remains fighting while giving her opinion) and the armistice happens. Then she goes to North Africa to continue the fight against the French.
(Anime and Manga only) Tanya is often mistaken to be even younger than she already is. She was growing up in an orphanage with little food and thus did not get the nutrition she needed. Children who starve during their early childhood have permanently stunted growth and remain small throughout their entire lives even if they receive enough nutrition later.
One of the bits of humor is how Tanya will completely misinterpret others' actions, and try to influence people to do one thing while actually influencing them to do the opposide. As a present-day salaryman, he fully admitted to being unable to connect with people and suffered/enjoyed many ASPD characteristics. Of COURSE Tanya would read and give social cues the wrong way!
The plot circulates around a suggestion Tanya's previous incarnation made to "Being X" upon explaining the reason of lack of faith in the world and how to restore it, prompting "Being X" to test out the theory of "Faith through Hardship" with Tanya as the test subject. If it actually turns out as a legitimate success and manage to reform Tanya's faith, what's stopping "Being X" from applying the "Faith through Hardship" approach on a global scale afterwards?
The anime has "Being X" actually state that the population of Modern Earth alone is too much for it to handle as it is. It makes one wonder what this being has in mind for those it can't handle. Brrr...
Global? Try multi-dimensional! (It did send Tanya's previous vessel's soul to a whole different world after all. How many worlds and realities is "Being X" actually in charge of again?)
Considering the Gods Need Prayer Badly trope, one wonders what would happen should Being X actually fail? Will he just stop maintaining the worlds he's in charge with? If worship is the equivalent of food to Being X, and the "rules" of the universe, whether physics or magic, are designed and maintained by Being X, what will happen to all those worlds if he decides to quit? At best, the "machinery" of the world manages to continue without anyone maintaining it for some time. At worst, reality itself may break down.