I've Been Killing Slimes for 300 Years and Maxed Out My Level

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.