Gather round friend's for these be important questions...
- Do the player characters derive their power directly from hosting an Atlantean soul?
This is something of a complex question to answer. The short answer is yes, the long is sort of. Technically every person in this setting has the potential for power, as every person falls into one of the five Denizen-races. However it is the infusion of the Atlantean souls that have brought that potential forward, because the knowledge of magic and how to tap into it has been lost for a very long time. Since the Atlantean souls know how, when they inhabit a body (and note that more Atlantean souls were released than just the six Story Souls, thus how other players can have souls) they draw on that power and 'form' the powers. This is why each of the Story Souls has a theme that those powers would develop from.
Hopefully that answers that.
- If yes to the above, are the powers possessed by the host individual necessarily the same or similar to ones the Atlantean soul once possessed?
It is reasonable to assume that the powers manifested in people inhabited by the Atlantean souls are either gaining direct knowledge from those souls or are getting some variation there of, thus the themes. Even characters without Story Souls should have general theme's in their power selection.
- Do souls consciously choose host individuals with whom they feel compatible (on any number of metrics -- personality, abilities, preferences, gender, etc.), or is it seemingly random?
It is mostly random. The Story Souls have generic things they picked out. Trillian had enough will power to not inhabit a female body, whereas Aeandra had the will not to inhabit a male body. Menaria knew the burden of the curse she had in her so she had the will to find a being hopefully strong enough to hold it as well, the Nephilim met her criteria just as well. Issail had enough will to maintain his birth right and would only inhabit a body with Atlantean blood.
Aside from that, it is mostly random. The souls do not have 'consciousness' until they have inhabited a body and been awakened. Which, at the start of game play, none of the characters will be. That's something that will take place shortly there after. Thusly, the characters at game play start have not manifested any of their powers sans perhaps some of the Denizen-race gifted ones, and those would be uncontrolled / accidental / not fully developed (Imori might 'dream projection', Fae just have never gotten lost and have always had an impeccable sense of time and space, etc).
- What is the nature of the bond? Does it merely grant the host individual a limited portion of the soul's knowledge, memories, and powers, or could it go beyond, into e.g. compulsion or bodily possession?
So this is something I was going to get into a little later, once we had a more solidified player base, and I'll save the mini-sheets for then... But basically how it players out is that once awakened each soul is going to act as a duality in their host....<taken from elsewhere>...you will actually be playing the souls. You'll need to detail them a little bit, and put some work into who they are and what they're like. The Story Souls obviously have some ground work already done but it can be fleshed out a great deal more to player desires. Once the souls awaken they will act as sort of a duality within the characters. They'll be able to communicate with them, and at times the souls may very well get yanked to the forefront of the characters and take control of the bodies...
...these are souls that are inhabiting the characters along side who the character was in the first place. Imagine every character in Pandemonium having a guardian, only that guardian is in their head and can sometimes take control...
In essence the souls will act as secondary characters that inhabit their host. They may not get along. They might mesh perfectly. They might have different ways of handling things. For the most part, GM Events aside, the souls will stay in the characters head. There's inner dialogue that can happen, basically everyone will have the chance to look at things from two perspectives instead of one. There will be moments where these souls are brought forward and made the focus for periods of time though. Giving everyone this sort of struggle for themselves feel. The souls aren't actively
trying to take over, but depending on the soul they might not be particularly thrilled to give it back either.
Part of the game will be the characters coming to terms and finding a balance with these second souls. Once they've done that they'll be able to harness more and more power, discover more about what actually went down and even do something about what's going on.
Hopefully that answers all of that. But more questions are always welcome. ^^