In the World of Sword and Magic as Space Marine - Chapter 79: I Have a Plan

What happens when a fanfic author with a habit of lying and scheming suddenly finds himself as a self insert during Duelist Kingdom? What happens when you have Yugi, Joey, Kaiba, and the rest encounter someone who knows all about every major player in their saga... and sees no problem with abusing said knowledge? Chaos, dear reader. Sweet, sweet chaos

What was originally an ordinary day, suddenly became a historical turning point. Enormous, mysterious Cubes appeared all over the world without warning and as if Judgement Day’s spears, inserted themselves into the blue planet.

From inside the enormous Cubes, endless streams of monsters gushed out alike raging tides, utterly defeating the unguarded armies of each state in the blink of an eye.

In order for humanity to preserve its final embers, the heads of states issued orders of retreat, to no longer attack the Cubes but rather to cling to remote cities, which they turned into self-sufficient survivor bases and around which they built 100-meter-tall Walls of Life!

Many years later, while bearing the heavy weight of history, the first expeditionary force brought back a world changing piece of information. The Cubes possessed exceedingly high intelligence and they regularly transmitted mission instructions to humans nearby. The mission rewards were incredible.

Since then, humans rushed out of the confines of the walls and once more set foot on the wasteland!

- Description from Novelupdates

Science and magic exist side by side in this world.

This is the peak of the science side with a curriculum for espers, Academy City. In this city where 80% of the population are students, the season has finally come when all residents are excited and fidgety!

It’s Christmas Eve.

Amidst the city showing a cheerful hustle and bustle, ordinary boy who can’t keep up with school, Kamijou Touma, also doesn’t intend to miss this event! He was hard at work in his supplementary lessons…

A backward glance from the default misfortune-prone bastard, the silver-haired sister freeloading in his dormitory, Index, in the heart pounding scene different from the usual, activates a new gluton skill!? While Kamijou tries to desperately stop that, Misaka Mikoto taken in by the Christmas Eve atmosphere appears before him.