I'm A Behemoth, An S-Ranked Monster, But Mistaken For A Cat, I Live As An Elf Girl's Pet (Manga) Vol 08 (Mature)

After being promoted to A Rank, Aria gets a request from His Imperial Majesty! Between an invitation to join the empire and the announcement of the return of the Four Demon Beasts, will Aria's party be up against the strongest enemies they've encountered so far? Yen Press
(W/A) Nozomi Ginyoku