Sixteenth Basket of Mantaos

Imagine being forced to live, after death, as incorporeal bodies trapped in a vast space of nothingness for thousands of years, with nothing to do but exchanging past memories with other cohabitants (read: weirdos).  Everybody wanted out, but there was no way to leave the Void... 
Until one day, a young man was finally summoned, as a powerful but reluctant mentor, by a bubbly and motivated but completely naive young girl. Baiyi, finally out of the Void, was the only one who could save all of the other 32 souls from their prison and his summoner might just be The Key to their freedom.
However, Baiyi had to use the techniques and abilities the other souls had taught him throughout the years, and together with his own extensive knowledge of anime and game tropes from his shady and dangerous past as an otaku, to face the biggest challenge of them all: training the clumsy young girl he was forced to partner up with… into a competent sorcerer!

EndlessFantasy Translation 

Why Did You Summon Me？

The only reason why Baiyi's plan did not hit any stump was because he had the help of a competent sleeper agent who was on the inside. So, as a reward, he loosened up the restriction on the man's powers so that he may return to Master-level.

"You have two choices now. You can stay by the Duke's side with your Master-level strength and Legendary-level experience, I think you're gonna earn quite a living with him. Alternatively, you can leave on your own and find a new way to live," Baiyi told him in a hushed voice.

"I don't mind working for you as long as you're still honoring your promise," the elderly replied sincerely.

Just Stick To What You’ve Been Calling Me