I have a question about the factions idea. Does this mean that we can't use champions like and who are all independent from factions?

Awesome that you're interested! Let me answer in three parts. First, I'll give you the short answer. Then, I'll give you the longer answer. Then, I'll comment on those specific Champions.

Short Answer

Not all Champions will end up in Factions. However, we give the factions some leeway to pull in more tangential Champions. For virtually every Champion, it's possible that they could end up in a Factions dispute on one roster or another, but yes, there are some who (due to their lack of strong affiliations) are less common to see in Factions.

We set up starting rosters for each faction at the start of each three-month arc. They're usually about 10 Champions per faction. During the course of the arc, factions can recruit new Champions; this is actually part of the strategic meta-game, as each faction's Summoners think about what they need most.

Each faction has a list of unlockable Champions for each arc, divided into "Core", "Secondary", and "Tertiary" categories.

• Core. Champions whose absence would be weird. Factions almost always start with at least most of these. (Example: Garen for Demacia.)
• Secondary. Champions whose presence would not be weird. Factions may start with some of these. They're more often recruited as the story progresses. (Example: Morgana for Noxus.)
• Tertiary. Champions whose presence might be a little weird. These are eccentric "longshot" Champions. (Example: Ezreal for Ionia in an arc against Noxus.)

Longer Answer

Let me link this post from the roleplaying forum, where I go into more detail about Core/Secondary/Tertiary Champions and the three criteria (Story, Feel, and Gameplay) that we consider when assigning Champions.

The Champions above

You can see how we've tentatively assigned many Champions on the Factions of Runeterra page. It's due for an update, but it may be illustrative.

Aatrox is a special case. Underdog factions are given a "devil's bargain" option every so often: they can invoke Aatrox and his dark powers, rendering them international pariahs but giving them great Military Strength. The Shadow Isles actually just made such a bargain in an interactive lore event unfolding as we speak. Some ties with Demacia. Might also fight for related factions against Noxus. Secondary Noxian: less because of her background, more because she's an evil little pyro-mage. Kind of an oddball; hard to fit in. I have some ideas for fleshing out his background which might make it easier to fit him in. Probably Bandle City, maybe also Freljord. Piltover. Could go Zaun if Zaun were to go "new leaf". Difficult. Probably a Tertiary Champion for certain orderly factions. Used to be an obvious SI Champion. Now he's an awkward anti-SI Champion. In the Factions verse, it was Bilgewater who sponsored her application to the League. Bilgewater is expanding into a larger maritime alliance, and Nami is trying to bring the Marai into the international community. Core Bilgewater at this point. :3 :3 A plot involving crazy rune magic might get his attention. Otherwise, a free agent. He misses his kind. T_T Might get involved on a Shuriman roster. Well, if there's an opportunity to fight the Batman, perhaps she'd join in.

why no piltover option?

Factions is organized into arcs. Each lasts about three months. For each arc, we select a set of playable factions (usually four), mostly by public poll. We limit it in this way to focus the story and facilitate match organization. (It's much harder to get matches going if people are spread out among ten different factions.)

Piltover has been in several arcs. They're taking a break for Nyroth.

Remember that your declaration only binds for the duration of the current arc. You can freely change factions when the next arc starts: actually, even if you want to stay with the same faction, you have to re-declare; it's a forced "blank slate" restart each arc, to keep the Summoner List up to date in terms of who's participating.

It's quite common. I can't count how many times I've had to last-minute substitute for a scored match. If you make yourself available, you will not be in want of a match to play.

no, but who wants to be known as the guy who can only play the champ best known for running away? LOL

wait, someone else holds that title... it was the whole time!