I've Been Killing Slimes for 300 Years and Maxed Out My Level, Vol. 2 (manga) — Kisetsu Morita

Azusa's life has gotten a little more lively since word got out that she's level 99, but she's been able to take it relatively easy with her new companions. Well, except for the ghosts in Halkara's workshop...and a run-in with the law...and an invitation to a demon castle? Still, even with so much trouble brewing on the horizon, Azusa's not about to forget the importance of taking life one step at a time.