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？

When she saw the grave expression on Baiyi's face, Laeticia was stunned for a minute before becoming serious herself. "I understand. I believe you."

She was obviously a kind-hearted girl who had little reservations in trusting an amicable man who had saved her life when she was in danger.

"Very well." Baiyi released his grip after a satisfactory nod. He added, "The evil that you felt earlier was a sign that the devils will soon infiltrate Arfin city. An uncommonly powerful demon had been roused—" He pointed at the Mage tower, still covered in thick smoke. "— there. I must stop it as soon as possible."

"I'll go with you!" She cried out in foolish courage.

The Technique We Have All Been Waiting For