Slime Taoshite 300-nen, Shiranai Uchi ni Level Max ni Nattemashita

Azusa Aizawa dies after years of overwork and decides that her next life will be the exact opposite of the one that killed her. A goddess gives her an immortal, ageless body as a witch, and Azusa settles near a quiet village where she farms, makes medicine, and defeats a few harmless slimes each day for spending money.

Three hundred years of that peaceful routine have an unexpected result: Azusa has accidentally reached level 99 and become one of the strongest beings in the world. She tries to keep it secret so that peace does not turn into another job, but rumors bring dragons, elves, challengers, and people in need to her doorstep. As her home gradually fills with a strange family she never planned to have, Azusa discovers that a relaxed life does not have to be a lonely one.