鬼滅の刃 3 [Kimetsu No Yaiba 3] by Koyoharu Gotouge

Now an official demon slayer, a determined young swordsman and his sister—who has been turned into a demon but still shows human emotion—undertake early deadly missions that test his fledgling skills and resolve; he hones his Water Breathing techniques, confronts brutal and morally complex foes, and repeatedly chooses compassion over hatred as he protects his sister and pursues a way to restore her humanity while learning the harsh realities of the demon-slaying world.