The Saga of Tanya the Evil, Vol. 7 (Light Novel): UT Sementem Feceris, Ita Metes

A sociopathic, atheist salaryman gets pushed onto a speeding train by the man he just fired, meets God, and then gets reincarnated as an 11-year-old girl child soldier in an alternate universe in World War I Germany. The eastern front is a place where soldiers never sleep and artillery guns howl without rest. This quagmire is where the Salamander Kampfgruppe has been hurled once again, just another cog in the grand war machine of their fatherland.

Still, there's only so much one unit can do. As the fighting ramps up with renewed enemy attacks and a brand-new weapon that pitches the Federation's quantity against the Empire's quality, Tanya faces one of her toughest battles yet, making a certain visitor's arrival a sight for sore eyes...