Ts Eiseihei-San No Senjou Nikki summary:

An ex-pro gamer of the FPS genre (♂) reincarnated in a fantasy world filled with magic... Only to learn that what greeted him was not a scene from one's dreams, but a muddy battlefield full of bullets flying to and fro! Moreover, he's now an orphan girl named Touri Noel?!After her aptitude for healing magic was discovered, she decided to volunteer in the army as a second-class medic, all to raise money for the orphanage where she was born and raised. However, without even getting magic training, she was attached to an assault squad, repeatedly fighting on the most cruel battlefields of the "Western Front."The mission given to her was to become the personal medic of the frontline's ace, Garback, and not let him die at any cost. But he turned out to be the worst commander, who will try to get results whatever the cost, even if it means the death of his subordinates!On the battlefield, mired in unreasonable orders and violence, Touri's fierce battle for survival continues...