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

Slime Taoshite 300-nen, Shiranai Uchi ni Level Max ni Nattemashita (スライム倒して300年、知らないうちにレベルMAXになってました) is a manga adaptation of the novel series written by Kisetsu Morita and illustrated by Shiba Yuusuke.

Synopsis
Ordinary office lady Azusa Aizawa died due to overwork. For that reason, when she finds herself reborn as an immortal witch with the appearance of a 17-year-old, she decides to live an easy-going life. Her main source of income is collecting magic stones that drop off the slimes that live in the nearby forest and selling them at the nearby village's guild. After doing this for the last 300 years, she's unknowingly become a level 99 witch, the most powerful of all.

Releases
As of March 2021, 8.5 volumes have been released.