The dynamic between Bang Chan and Felix in fics tends to follow a few pretty strong archetypes, depending on how a writer interprets their real-life 'dad and sunshine' energy. A huge chunk of stories frame them as soulmate-level platonic brothers—Chan is the exhausted, overprotective leader who carries the world's weight, and Felix is the emotional core who pulls him back from the brink with pure sunshine and homemade cookies. It's the classic found family trope dialed up to eleven, and honestly, it works because their offstage chemistry feeds it so well. You see a lot of hurt/comfort scenarios built on this: Chan working himself sick and Felix forcing him to rest, or Felix having a crisis of confidence and Chan giving the 'you're my light' speech. The physical affection they're known for gets translated into endless couch cuddles and forehead touches that are somehow both familial and intensely intimate without crossing a line.
But then you have the other major lane, which is the slow-burn romantic pairing. This often starts from that same intense brotherly bond, but adds a layer of simmering, unspoken tension. The plots frequently involve pining—one of them, usually Chan, realizing his feelings aren't so brotherly anymore during a late-night studio session, or Felix getting jealous over something small and confusing about why it hurts so much. The fandom loves to play with the height difference and the voice contrast; you'll find a lot of scenes where Felix is the one to initiate a kiss by pulling Chan down by his shirt, subverting the 'hyung' dynamic in a really sweet way. I've read some that flip it, though, where Felix is more of a secretly confident force beneath the cute exterior, and Chan is the flustered one. It's less common, but it's a fun twist on the expected power balance.
Ultimately, whether it's platonic or romantic, the core interaction is always about profound, unwavering support. They're each other's anchor. Even in AUs where they're vampires or CEOs or superheroes, that dynamic remains: Chan provides stability and a safe harbor, Felix provides warmth and a reason to keep fighting. It's less about grand dramatic conflicts between them and more about how they face external conflicts together as an unshakeable unit.