I'm not entirely sure as I haven't read it yet, but it's likely that the ronin himself is a main character.
Since it's a ronin - focused novel in the Star Wars universe, the main character is surely the ronin. However, in the Star Wars style, there could be a droid sidekick that provides some comical relief and technical assistance. There may also be a Jedi - like figure who either helps or challenges the ronin. And of course, there could be some villains, like a group of bounty hunters or a dark - side user who are after the ronin for their own reasons, be it for his unique abilities or something he possesses.
The main character is probably the ronin. And there might be other supporting characters such as those who are on his side in his journey, like a fellow outcast or someone he meets along the way who has some knowledge or skill that helps him. There could also be antagonists, perhaps a group or an individual who is trying to stop the ronin from achieving his goals, maybe a Sith - like character or a power - hungry warlord.