Academy Heroine's Right Diagonal Back Seat - Chapter 100

After the death of his parents, Adam Hall was forced to enlist in the army to fight against enemy kingdoms.He later joined the crown prince's army as a commander.Until he became one of the ten strongest people on the continent.He started a war to avenge his fallen family, but failed and lost his life.Just when he thought it was all over...“What? Am I alive?”He found himself young again, with his memories intact.Armed with his knowledge of the future and a plan, Adam set out on his journey to make amends for his regrets and change everything.

The Supernatural era descended, the rules changed, mystery arrived, and the world altered. Countless ruins of civilization emerged, and an abundance of Heavenly Materials and Earthly Treasures lay at everyone’s fingertips. Radical faction, “This is the best of times, entering a new world, excavating relics, mass evolution!” Conservative, “This is the worst of times, with countless monsters outside, once you leave the Safe Zone, extinction awaits humanity!” … Meanwhile, at a remote ruin, Lu Yuan successfully discovered new treasures and sought after the mysterious wealth, desperately trying to contact his fellow Earthlings. “Found a communicator, can it get through?” “Hey, humans—I’m almost becoming a god, and you’re still hiding in the Safe Zone?”

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

Set on a giant, almost finished bridge between Sadogashima and Niigata. Abandoned by the government, the bridge, and the giant man-made floating island at the center, has become a city of criminals and societal drop-outs.

Set in the same world as Durarara, but 15-20 years later. There is almost no overlap between Etsusa Bridge and the other novels.