[houkoholic]

It's hard to think that Kouga would be Seiya's son, since the mother would be hard to write about.

It can't be Saori/Athena because it goes against mythology (Athena is a virgin goddess), and Shaina obviously not married to him or anything. This leaves Seiya's childhood friend who hardly anyone remembers her name now but if they write that in the story I don't think the fans could accept it. In fact I think the fans enjoy seeing the unresolved romantic tension between Seiya and all the females he is close to and setting it in stone would ruin this, so I doubt Kouga would turn out to be Seiya's son, possibility is too low.

As for why Kouga can use the meteor first - the show made it a point that he's seen Seiya perform it, plus Seiya was obviously talking to him when Kouga puts on the pegasus cloth, so it's not hard to imagine that's how it was passed on to him. Also when you have Shura passing the Excalibur to Shiryu in the original this is hardly surprising.... definitely a "it's just is" plot moment, especially since they are making a point that Kouga is Seiya's spiritual successor.