You might want to consider doing a gantz review, it's plot is a lot like battle royal's except with a dash of sci fi.
The main character, Kei Kurono, is your typical teenager. Until one day, when he's persuaded by an old friend to help a homeless man off the subway tracks. The homeless man is saved, but they didn't get out in time and they both died. They then find themselves trapped in a room with strangers. As the series goes on they find themselves to be trapped in a sort of game. In which they have to use high tech weapons to kill aliens before they timer runs out, or they all die.
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