>Does he really fit with the rest of the crew? I mean does he even fit into Shonen in general?
That's the entire point of his character, he doesn't fit.
In a world of super powered wonder people who laugh in the face of death and charge towards the ends of the earth, he's a coward without any abilities.
He's only tagging along with the crew because they're the sort of people he wishes he could be.
Oddly enough, even though he becomes the man he wants to be, a brave man of the sea, he can't see that himself because he's always comparing himself with fucking invincible ubermensch.
It's just a good thing Sogeking's around to show that a normal guy with a slingshot can keep up with the big guys and kick ass.