I started it a few years ago, and I can't say I remember too much about it... What I do remember-

I 'think' it starts off on a ship? And there are people on board that have powers. The main character (one of them?) has the ability to make things just fall apart. He uses it on a box that is actually holding another person, who I think was supposed to be super dangerous.

Within the next few chapters, they get to the prison, or whatever it is, and the people let them run loose, and I think a lot of them just start killing each other. It might have been some sort of test thing?

That's the most I remember.

Editted to mention: Ignore the 'fic' at the end of the title. I meant manga. Too much time on fanfic sites

I believe you're looking for Area D - Inou Ryouiki

https://www.mangaupdates.com/series.html?id=75545

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Cynicism at its best.

Gah, I actually looked at that when I was trying to find it, and automatically assumed it wasn't it. Thanks