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？

"What happened? Who did this to you?" Baiyi hurried to Anna and reached out to pat her head, but she ducked and hid behind Nota. Anna peeked out from behind Nota, looking at Baiyi in fury.

"Hey, hey, what's the matter? Someone bullied you, didn't they? Well, tell me who its and lemme at' em!" Baiyi gallantly said.

Nota sighed. She took the jet-black rock from Anna, raised it to Baiyi's face and pulled out a tag that was stuck to it. "Mentor, do you remember that it was I who brought you this ore? I brought it back from my last excursion to be appraised. Shouldn't it be staying put in your lab?"

"…Oh. Ohh." Baiyi froze. He had just remembered that the black rock was the first thing he threw into the scribble.

"I knew it! You… B-big Meanie!" Anna whispered from her spot behind Nota's back, her eyes narrowing with distrust.

It's A Key Invention!