Sun is shown to be fun-loving and mischievous, with little regard for the law - stowing away on a ship, thanking the crew for the ride during his escape, throwing a banana peel in a detective's face, and stealing apples. He has a lot of self-confidence,.
In conversation, Sun is very laid-back and casual. He is also kind and patient, willing to listen to Blake Belladonna's story and waiting for her to do so for nearly two days, bearing with her "small talk and weird looks". He is not afraid to give his opinion and has a dislike for those who regard themselves as "holier than thou", or who "use force to get whatever they want", such as the White Fang.

Reference for those who has not yet heard the voice:
https://www.youtube.com/watch?v=am1Uas6NB_U