Renkindžucu to, jósei to (E01)

"We'll remain best friends forever." The promise made between four young friends were engulfed by the flames of war. During the Hundred Years' War in the 15th century, there was only one way to save a comrade fallen by the assault of the English army: bequeathing the the legendary alchemical substance "Philosopher's Stone" into the body to turn her into an immortal superhuman "Ulysses." The young Montmorency devoted himself to the forbidden research, when the fairy queen Astaroth appeared before him... (Crunchyroll)