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

Aizawa Azusa accidentally works herself to death at 27 years old; she is reincarnated as an immortal witch and finds the experience of killing slimes for 300 years makes her the strongest adventurer in the world which results in daily challenges.

After becoming the strongest in the world before she even knew it, Azusa entered into a new lifestyle with her first pupil, Laika the dragon, and discovered fun and enjoyment in it that she hadn't known before.

Just as peace is beginning to reign in Azusa's home, a young elf named Halkara shows up pleading for her help.

Leila is getting married; Azusa and her friends set off to visit Mount Rokko, the home of the Red Dragons.

Halkara has built a new Nutri-Spirit factory in a nearby town and is now regularly going there from the cottage in the highlands, but she comes home exhausted every evening.

Azusa receives an invitation from Beelzebub to attend a ceremony in the land of the demons; it seems she earned a favorable reputation with the demons after stopping the conflict between the two Dragon clans in Laika's homeland.