User blog comment:IE2555/A discovery on the Official Website.../@comment-1839918-20140213021429

Based on what I know, I'll try to clarify each of these as best as I can.

Sivir and Nasus worked together at one point, and both live in Shurima Desert, which has something like a whole 4 people in it.

Ahri and Wukong were both animals who obtained humanity somehow, and are learning to be more "human" (The reason Zyra wouldn't be here is because of her malevolent nature)

Ryze despises the use of magic for chaos and destruction, while that is pretty much everything Brand does

Malzahar himself brought Kog'Maw into the world. Kha'Zix and Cho'Gath arrived of their own will, and might not even know Malzahar that well.

Not quite sure here. Maybe Vladimir ticks Darius off. Or he might think Darius wastes blood the way he just chops people up.

Renekton and Xerath worked together to fight the previously mentioned duo of Sivir and Nasus, I believe

LeBlanc and Elise are both women of high rank, skilled in magic, who enjoy decieving and betraying others.

Zed and Syndra, both being from Ionia, share a similar point of view. And fighting for Ionia doesn't necessary mean they all fight for the same cause (Ashe, Sejuani, and Lissandra all fight for the Freijord, despite being enemies)