If I were naming them, I'd be sorely tempted to call them Thor (boy) and Loki (girl), and never mind the genderbending. OTOH, we do have a Loki right now, and... let's just say he was an excellent example of "be careful what you summon" for a while. :-)

Other ideas: Logan & Mariko, Estel & Arwen, Robin & Marian, Chaz & Hafidha (possibly too obscure), Barnabas & Josette.

My primary associations for "Harlequin" are either Punch & Judy or Batman, and neither of those is helping with "Harrison".