Wei-Chen is just about the coolest character in the book. Yeah he can't dress or style his hair (2.62)—even when he becomes super-gangsta toward the end of the book—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" (5.22) for not volunteering with Amelia to take care of the animals in biology class after school. He gets Jin to pursue his dreams, like when he urges him to ask Amelia out, saying "'Again is a chance for your lifetime!'" (5.85). He covers for Jin when he needs him, even though it goes against his principles, like when he tells Jin "'Sigh. Fine. For you, I tell lies'" (8.4) and tells Jin's mother that Jin's with him while Jin is on a date with Amelia.
He also will never try to kiss the girl Jin likes (can't say the same for Jin, unfortunately) even while stuck in a closet with her for an afternoon. Instead? He pumps Jin up. Wei-Chen tells Amelia all about Jin's good side, like when Jin "'show [him] how things work in America. He help [Wei-Chen] with [his] English. He teach [him] hip English phrase like 'Don't have a cow, man' and 'Word of your—' no, no… 'Word to your mother'"(5.72). He admits to Amelia that "'If [Jin] was not here, I don't know. I would have been so lonely'" (5.73).
Who could not like Jin after Wei-Chen's awesome description of his and Jin's friendship? What Wei-Chen reveals to Amelia completely primes her to say yes when Jin finally asks her out on a date. He's that instrumental of a character.
In fact, you can even consider Wei-Chen an honorary major character: just like Jin and the other protagonists, Wei-Chen goes through some major transformations too.
It starts with the moment Jin plants a big wet one on Suzy and Wei-Chen gets upset as a result. But even as upset as he is with Jin, he's so generous. He tells Jin:
"If you had feelings for [Suzy], you could have told me. I would have listened. I wouldn't have turned my back on you. Now you've broken my heart more completely than Suzy ever could. Jin… you and I… we're alike. We're brothers, Jin. We're blood." (8.117-8.119)
How could anyone turn against someone as vulnerable and honest as Wei-Chen? Jin can, that's for sure. What he says in response—"'Maybe I just don't think you're right for her, all right? Maybe I don't think you're worthy of her. Maybe I think she can do better than an F.O.B. like you'" (8.123)—causes Wei-Chen to do something he's never done in the book up until this point: punch Jin hard in the face (8.124). Not that we advocate violence here at Shmoop, but we can totally understand why Wei-Chen would be driven to the point of punching Jin for Jin's words.
The next time we encounter Wei-Chen, he's rolling up outside the Chinese bakery/café in a bass-thumping rice rocket (check out the "Shout-outs" section for more on this) and Asian gangsta clothes straight out of the 1990s (9.106-9.113). We know he's not really a wannabe gangster. We know he's just rejecting his true self (a follower of Tze-Yo-Tzuh) because, as he tells his father the Monkey King, "'I've found humans to be petty, soulless creatures, the thought of serving them sickens me'" (9.66). Guess it's his turn for an identity crisis now that Jin's on the path toward personal peace.
Who is Wei-Chen really? We think he's the earnest, geeky, nice guy who, after Jin's humble apology to him, launches into a Top-Chef critique of the pearl milk tea at the Chinese bakery/café, saying "'The tea itself has an oily taste, like they were stir-frying something nearby when they made it. The boba reminds me of rabbit crap'" (9.121-9.122), and then invites Jin to try some real pearl milk tea at a little place down the street (9.123)
The message to Jin? All is forgiven.
That's just how Wei-Chen rolls. He's not about holding onto anger if he sees someone actually trying to be good, like Jin when he makes his apology.
That's why Wei-Chen's cool. He may seem awkward at first, but he doesn't really care what anyone thinks—he just goes on being the good kid his papa monkey raised him to be. Which makes him kind of like a hero in our book.