TS衛生兵さんの戦場日記
TS Eiseihei-san no Senjou Nikki (lit. TS Medic's Battlefield Diary) is a Japanese web novel turned light novel series written by Masaki Tama and illustrated by [[Kureta_(nikogori)|]], with a manga adaptation by [[Mimishiki]].  The series is an isekai set in a WWI-ish war with magic.  The TS in the title is short for Transsexual, which refers to the Transsexual Fantasy genre, ie series involving genderswapping.

The story follows [[Touri Noel]], a 15-year-old girl who was a male in her past life and a skilled FPS player.  After learning she could use healing magic, she left the Noel Orphanage and volunteered to join the military following a childhood friend.  Assuming she could make use of her FPS knowledge to succeed on the battlefield, she quickly learns the reality of war is a very different and very brutal thing as she tries to stay alive.
ts eiseihei-san no senjou nikki