Inspired by the old speculation about Lucy based on the infamous trail of red footprints, I... had something in mind but can't write prose to save my life (unless RPing in prose of all things), so I open the pairing idea up to whatever you will do with it, even if it's just a roleplaying fantasy (i.e. Assassin!Rebecca x captive Templar!Lucy) between the two...

Bonus points if Desmond for whatever reason comes across the pairing (i.e. sees them kissing, but Rebecca in blue and Lucy in red) and reacts by fleeing TO the Animus, not from it!