If the upper Aeon is male and the Overdrive Aeon is female, then the upper half would technically be the Animus, the traditional representation of the rational masculine mind, and the Overdrive would be the Anima, the traditional representation of the animal feminine mind.

I always thought it was a little twisted of her Fayth to suggest the best way to save Seymour's reputation for posterity was by having him (SPOILER)die. Of course, this is well in line with the morality in Spira, where a personal sacrifice for the greater good was the ideal for a Summoner.