Answer: Wei Chen is a foil
Explanation: In fiction, a foil is a character who contrasts with another character, usually the main character to highlight particular qualities of the other character. In some cases, another argument can be used as a foil to the main plot. This is especially true in the case of metafiction and the "story within a story" motif.
Wei-Chen is just about the coolest character in the book. Yeah he can't dress or style his hair and sure his English is broken, but he's the kind of supportive friend you want in your corner, especially when things go bad.
He's honest, like when he calls Jin "a cowardly turtle" for not volunteering with Amelia to take care of the animals in biology class after school.