Think of the most racist, surliest person you know and you've got yourself Jolly. He's the classic villain to Manjiro's classic protagonist. In fact, he's almost cartoonish in his villainy, like when he jumps Goemon and Manjiro and tries to steal their money, while calling them things like "naked cannibals," "monkey trained to snitch things," and "illiterated savage boy" (2.11.13-15). Yes, he says illiterated. But misunderstood words aside, one thing's super clear here: Jolly is nasty.
But even this mean dude undergoes a change—or at least, he comes around to Manjiro the second time they're on a crew together. And this is because he's the type of guy who can be influenced over time. While our good characters stay good (read up on Manjiro and the Captain for more on this), here we have a bad character who actually changes a bit.
Here's what Jolly says about Manjiro, when Manjiro's up for the position of harpooner (Jolly's position):
"I gave him a wee bit of a hard time, I warrant."
"And I was none too pleased to see him aboard the Franklin, truth to tell. But I will admit he has courage, showed when he flung himself into the sea after our supper. And he has nerve, demonstrated tonight in his going toe-to-toe with our former captain. The fact that he can last an entire watch with Danny-boy there," he jerked his thumb to indicate Daniel, "shows he has patience. And he can put up a fight when necessary which I know from… personal experience…. So I guess my vote is 'aye.'" (4.31.35-37)
Jolly wasn't known for his honesty before, but this little speech of his on Manjiro's behalf shows he has more character than we might expect. Not only is he honest, but he has the strength to speak positively about someone whom he initially wrote off as useless (to put it lightly). Additionally, in this moment Jolly is giving up his job to Manjiro. So yeah, on a number of levels the generosity of spirit here is totally unexpected.