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

A very ordinary company OL (Office Lady), Azusa Aizawa died from overwork. Because of that, she decided to live a leisurely life in a house in the mountains as an immortal, 17-year-old witch in her next life. Her main source of income is to defeat slimes in the nearby field to acquire magic stones, which she sells at the nearby village's guild. Other than that, she passes the time collecting medicinal herbs, and became known as the respected and trusted "Witch of the Highlands." However, as a result of farming slimes every day for 300 years, she gained too much experience, and unknowingly became level 99 – the world's strongest witch.