How to write an introverted main character with accidental charisma
I’m planning a medieval-style fantasy epic in which a young protagonist is plucked from his humble life, acquires great powers, and ultimately saves his civilisation from the Big Baddie (a politically manipulative dragon). My MC’s personality is quiet, dreamy, introverted, and a little bit quirky. I imagine him as having some mild autism spectrum attributes but will probably play this subtly, if at all, in the written version of the character.
I’m working pretty hard on defining the MC’s motivations clearly, because his tendency is to be passive. He has no ambitions to heroism or adventure and spends the first third of the story just reacting to unusual events (with one important exception). After some terrible things happen, he spends the middle third trying to find answers, but still doesn’t have a clear goal in mind. Only by the last third does he realise that he needs to be a hero and that nobody else can do the heroic thing.
I want to make sure that my MC is not overshadowed by my secondary characters, some of whom seem to be more proactive or have more “colourful” personalities which the reader might naturally find more interesting. In particular, I want to convey that other characters are drawn to the MC, not because he’s conventionally charismatic but because of a special something that makes people like him and want to help him, perhaps without realising why. Local folks are starting to put their hope in him by the middle third and he's a full-blown national icon and rallying point by the end, despite him just trying to get on with the job of fixing the world with his growing magical powers. He's not interested in fame - he just does what he needs to do in the moment, based on what knowledge and ability he has.
My question might actually be twofold because I don’t know the answers to either of these things: What aspect of his personality gives him this compelling something, exactly? How do I convey that in my third-person narrative? (by which I think I mean, How do I make the reader feel the same way about him?)