A Slow Life After Being Expelled, Which I Never Wanted? I was Supposed to Have Retired, but Somehow I Ended Up Becoming a Beautiful Girl's Mentor, and for Some Reason, I Feel Really Nostalgic.

Reito Harukaze, who had climbed to the highest rank of adventurers, had retired. One day, as he was thinking of living a quiet, retired life, a beautiful gal named Karen Hiiragi appeared before him. "Hey, mister, buy me a meal!" Upon hearing that Karen was in trouble with money, Reito decided to give her a basic lecture on dungeon conquering. "Thanks to you, I was able to conquer my first dungeon! Master!" He actually wanted to retire and live a slow life...