Sent to the Future?

It's a normal day in the 3-E class. The students are training, some are attempting to kill Koro-sensei, and others are asking for his help with their studies.

Meanwhile, the government was experimenting on a new weapon to possibly kill Koro-sensei. However, said weapon did not turn out to be what was expected. Once it was exposed to the class on this supposedly normal day, a bright light flashed over them. Fearing the worst, Koro-sensei went at Mach 20 to gather and protect his students and fellow teachers from the light.

Once the light was gone, the class noticed they were in an unfamilar place. They appeared to be in the middle of a road in an unfamiliar city. It was as if a huge earthquake destroyed everything: roads, buildings, cars, etc.

The class looked around confused, wondering how they had gotten to these ruins. They all knew one thing for sure: getting home would not be an easy task.

Suddenly, the clashing of swords told them they were not alone.

So I was just scrolling through my recommendations when a crossover book with two animes I liked popped up. I read it and then got interested in other crossovers so I started browsing but couldn't find with animes I really liked. So I decided why not write them myself? As of right now I have no idea how I'm gonna make this story work but it'll come to me. There may be ships and if there are, they're more than likely BL ships. Also I'm basing this off of the anime for both but I may add some things from the manga for Owari no Serafu since I'm caught up with it. I'll try to refrain from that though. Anyways, I hope you enjoy this story made from my boredom.