I had the idea of a Chosen One from ages and ages ago who gets told as a kid, hey, Chosen One, guess what, you get to go on an adventure to become the Chosen One who'll defeat the Dark Sorcerer and save our Ancient City! So he goes off, but it turns out it's kind of a bad idea to leave Chosen Oneing to a child, and he spends the next 9 or so years getting sidetracked by sidequests and, not really thinking things through, when he's about 17 gets stuck in a magic lamp by some evil spirit or maybe just a hobo or something. Then he spends the next thousand years on a small, lotus-eater type island in the middle of an endless ocean at the bottom of the lamp, not really doing much, completely misses his Chosen One deadline, then finally gets let loose in modern times.
I'm thinking personality-wise, you get this guy who's honest-to-god sweet as a button, had about a thousand years to mellow out, but is extremely susceptible to praise, is a little easily manipulated, will fall in love at the drop of a hat. Probably more of a follower than a leader. And when he gets out of that lamp, suddenly, for the first time, absolutely no one is expecting anything from him, no one really cares who he is or what he does, so he's really just having a blast with life, y'know? Hey, why don't I do this tournament thing, I bet I might meet some Cool New Friends wouldn't that be just the darndest thing? But also in a lot of ways he's a bit of a useless potato, and is mostly good at dumb sidequest related things, like tracking down lost pets, filing taxes, things that are normally just really grueling and frustrating to finish off.
For fighting, I liked the idea of him figuring out the basic process for the lamp's ability to trap things inside, like, being able to temporarily seal away things like pain, or injuries, or even an entire attack inside little vases and jars, can open it back up again if he wants, ot it just busts out naturally within a few minutes. Totally just spitballing here though.
(Drew this up as a quick design sketch too.)