Saga of Tanya the Evil

Saga of Tanya the Evil, known in Japan as Yōjo Senki (幼女戦記, lit. "The Military Chronicles of a Little Girl"), is a Japanese light novel series written by Carlo Zen and illustrated by Shinobu Shinotsuki. Enterbrain has published seven volumes since October 31, 2013. A manga adaptation with art by Chika Tōjō began serialization in Kadokawa Shoten's Comp Ace magazine from April 26, 2016. An anime television series adaptation by NUT premiered on January 6, 2017.

Plot
For having insulted God, an arrogant Japanese salaryman in the moment of his sudden death is sentenced to be reborn in an alternate universe similar to 1920's Europe, in an empire torn apart by countless wars with all nearby countries. The salaryman is reborn as Second Lieutenant Tanya Degurechaff of the Imperial Army, a 9-year-old soldier girl. Plus this, according to God's words, if she's not able to die a natural death or she refuses to have faith in Him, her soul will leave the circle and be sent to hell for the countless sins that Tanya has committed in her previous life. In search for an escape, Tanya decides to enter into the Empire's Mages Division, hoping to reach a high enough rank as fast as possible to remain far from the battlefield and in this way avoid the risk of being killed. Even if she's now forced to speak with a young girl's lisp, Tanya soon turns into a ruthless soldier who prioritizes efficiency and her own career over anything else.

Official
Official anime website

Other Sources
Wikipedia