Gakuen Toshi Z

In the floating in space academic city of Z students compete against each other using their own robots. This year just one day before competition the Red team members got intoxicated by food poisoning. Just one red team was intact. So the rules were changed - if Red team gathers five crystals scattered throughout the school - it wins. Otherwise white team wins. And now single Red robot faces 20,000 white robots.

[From vndbreview]