I think it was Cy that I had a whole pair-off-Org-by-element thing. Or DM. Or TIP?
Fuckit, can't remember. Anyhoo, I'm a player of Sword and Children of Mana (I can't say Secret; I never beat the bird boss in the Gnomes' hobble...I was young and ignorant) and they have their 8 spirits.
Undine - Water
Salamander - Fire
Gnome - Earth
Luna - Moon
Shade - Darkness
Wisp - Light
Dryad - Wood
Jinn - Wind
Now, in Sword of Mana, Wisp and Shade had a canonical conflict with each other. Wisp is Light, Shade is Darkness. Well all right. Children Of Mana have a Gem called the Light & Darkness Flaw (the Flaw Gems prevent status effects and raises risks for those they don't prevent). Again, Shade and Wisp pair off, which suggests common links between those that pair off.
...which is Xemnas and Roxas. First and Last. Alpha, Omega. The Light and the Lack of it.
And because there's also a Water & Fire Flaw, Earth & Wind Flaw, AND Moon & Wood Flaw.
Moon and Wood. Saix and Marluxia.
Axel/Demyx was obvious.
Xaldin/Lexaeus rounds off the main elemental quartet. Which leaves Xigbar, Vexen, Zexion, Luxord, and Larxene.
Only Larxene and Vexen are left of the physical elements, and are of lesser status than their four big brothers. That pairs them off.
Time and Space go together like peanut butter and cream cheese. So, Xigbar/Luxord.
Which leaves wee Zexion to his own devices. The little question mark. >.>
So, yeah. Saix and Marluxia have some sort of elemental connection. Earthy versus Heavenly and all that. So says SquareEnix themselves, if not subtly.