Niv Squared

Neve, an enemy of this future Earth nation, is sent back in time to right the wrongs of her advanced society, wrongs that have left everyone on Earth immortal and untouched. Only she and Paul, a young boy from 1987, can stop the impending massacre at lunchtime and right the wrongs of mankind's madness. A mysterious secret locked in Paul's mind may be the key.

Things get complicated when everyone on Earth in the future tries to stop you, and the rules of time travel depend on how charismatic you are.