Ever notice how Heero and Relena have the same profile? It's the same in the Manga too (Although a lot of people have said Relena is a lot cuter looking in the Manga, but that's why Manga are so good, they do a better job). I wonder if they did this purposefully as a metaphor. It's believed that most twins are linked, well Heero and Relena look a little like Twins, so maybe it's metaphorical for them being bonded in some special way. Lovers, Adopted Siblings, whatever kind of bond you can think of.