Before exploring my answer to your questions, I think it’s very important for me to remind myself what a theme is, and how it differs from a plot.
A plot is a series of events happening in an (often) sequential order. A theme is the underlying message or thought that drives (or does not drive) these events. Another way to look at it as the plot is the “what” of a story, whereas the theme is what I consider the “why” of the story, making up at least one character’s motivation to drive him along the plot. Without a theme to hold it up, a plot turns into what is essentially a shopping list of events happening without any clear rhyme or reason.
In the context of roleplay, it’s a complicated issue because several authors are coming together to further a plot, or several plots, and different characters will all be driven by different motivations. That being said, I think each individual character should operate off of a simple premise that explores a particular topic inherent or otherwise relevant to them. What is interesting for me, though, is if you actually begin to treat your character as a real person, you realize that they don’t even adhere to a single theme.
For example- Karnum is a Death Knight, risen during the Third War in a similar vein to Koltira Deathweaver (ironically a character I wasn’t aware of until long after I decided this backstory). Coming to grips with who he is, what he’s lost, and what he can and cannot do as an undead warrior who sowed chaos and despair, is a major part of his character. But that’s just one of many facets to his personality and story. Being slain and risen before the notion of Sin’dorei was conceived gives him a unique perspective on his ‘people’, who he may associate with on a surface level, but internally feels resentment towards for falling so far in the first place.
All of this clearly reads like my character is a really dark and brooding individual, but that isn’t always the case. Certainly he isn’t jovial by any stretch, but he has an understated love for being bitterly sarcastic about his lot in unlife. Actually, a lot of my characters engage in dry sarcasm, but anyways.
If Karnum’s “plot” is that he’s a Death Knight roaming Azeroth and trying to find a place for himself, then what gives this goal legs to stand on is his desire to understand what Undeath truly means for him as an individual, and either accepting or rejecting the premise that his people have changed.