S-Rank Monster no "Behemoth" dakedo, Neko to Machigawarete Elf Musume no Pet toshite Kurashitemasu

A knight dies protecting humanity and awakens in a dungeon as a Behemoth, an S-rank monster of the very kind he would once have considered an enemy. There is one complication: he is still a juvenile, and his body looks almost exactly like an ordinary orange cat. When the elf adventurer Aria finds him badly injured, she assumes he is a harmless animal, nurses him back to health, and names him Tama.

Tama accepts his strange new position and recognizes Aria as the master his old knightly honor demands he protect. Beneath the adorable appearance is a monster capable of acquiring the abilities of creatures it consumes. He follows Aria into dangerous adventures while keeping his true nature hidden. To her, he is an unusually capable pet; to Tama, every threat near Aria is another battle worthy of the life she gave him back.