I’ve Been Killing Slimes For 300 Years And Maxed Out My Level Vol. 12 (Light Novel)

Azusa Aizawa is an extremely ordinary office worker who dies of overwork at the age of 27 only to be reincarnated into another world as an immortal witch. Reflecting on her previous life, she begins living a leisurely and slow life in the remote highlands. In her day to day, she earns coins by slaying slimes, makes potions like a witch, takes care of the village at the foot of the mountains, or simply enjoys doing nothing at all. Her life continues like this and she becomes known as the “Witch of the Highlands."
After 300 years, due to all the experience she has accumulated killing slimes she reaches level 99 and becomes the strongest person in the world. As rumors spread, her life begins to get livelier as not just adventurers confident in their skills but also dragon girls begin appearing and challenging her to fight. And even mysterious monster girls show up calling her “Mom”!
Notice: This book is written in Japanese.