Finding a good Chika x Riko friendship and rivalry fic is like looking for a specific shade of paint – most stuff skews heavily romantic. The non-ship focused ones tend to treat their dynamic more like background texture for the bigger 'Love Live! Sunshine!!' idol plot, which is a shame. Those two have such a rich tension right from the start: the hyperactive, instinctive dreamer versus the disciplined, anxious classical musician. The best fics I've read dig into how that rivalry isn't about beating each other, it's about mutual ignition. Riko's frustration with Chika's chaos secretly pushes her to be less rigid, while Chika's awe of Riko's skill makes her work harder to be 'good enough' to stand beside her.
It's a dynamic built on intense observation and a weird, competitive empathy. A story that nails it might show Riko noticing Chika practicing a dance move wrong for the hundredth time, and instead of just correcting her, feeling a spike of irritation that melts into... I don't know, a kind of protective frustration? She starts practicing with her, turning it into a silent duel where they're both trying to outlast the other, but the real win is Chika finally getting it right. That's the core of it for me: their rivalry is the language of their care. It's how they communicate respect without having to get sappy about it, which neither of their personalities would allow.
I wish more writers would lean into the awkwardness of it, too. The fics that feel real show them misunderstanding each other's motivations, getting petty over small things, and having to rebuild that fragile trust after a clash. It's messier than pure friendship, and way more interesting.