Let's say that this is going to be Misaki from the beginning of the main series and Lelouche from before the Black Knights betrayed him.
Round 1: Fist fight, no powers
Round 2: Both characters are in a mix of Academy City and whatever city Ashford Academy is located in; they are each trying to safely capture the others (though in Misaki's case, she's after Zero rather than Lelouche). Assume that the Zero helmet can provide immunity to Shokuho's telepathy unless she's within range of his Geass.