Lloyd/Kratos
Kratos is a father, so we know he's had sex before, and because SPOILERS, he theoretically could've had quite a bit of it. Lloyd's pretty popular with the ladies himself.
Kratos/Zeus
Forget what I said about Tidus/Jecht; this is our contest's winner. Zeus is legendary for screwing anyone and everyone. Probably 90% of the gods and goddesses and legendary heroes in Greek Mythology are his children.
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http://www.youtube.com/watch?v=2fB2P4Scf8E
Ancient indeed.