I'm a Behemoth, an S-Ranked Monster, but Mistaken for a Cat, I Live as an Elf Girl's Pet, Vol. 9 (manga‪)‬

A Fur-rocious Battle Comes to Its Climax!

Aria and friends, now members of the Imperial Heroes Brigade, return to the Underground Labyrinth on a quest to take down the catastrophically powerful Four Fiends! The first of the resurrected demons sends vicious beasts after the party. While Aria goes all out using the skills she gained from training with the Sword Saint, Tama feels his own power awakening! But will his sudden transformation let the cat out of the bag about his true identity as a behemoth?