If you're specifically hunting down Kinger and Jax stuff from 'The Amazing Digital Circus', you're going to be living on Tumblr and Archive of Our Own. Tumblr's the weird, beating heart of it—the memes and headcanons start there, and the fic often follows in these wild, snippet-style posts. You've gotta follow the right blogs and get into the tag game, which can feel like herding cats sometimes, but that's where the raw, immediate fan reaction turns into story ideas. AO3's where those ideas get fleshed out into proper narratives. The tagging system is a godsend for finding the specific dynamic you want, whether it's rivals-to-whatever, absurdist horror-comedy, or pure crack.
What I've noticed, though, is that the really sharp, meta stuff about their dynamic—the whole predatory clown versus anxious king chess piece thing—tends to bloom on AO3. Writers there love picking apart the psychological horror underpinnings of the show and applying it to their messed-up relationship. You get these brilliant analyses disguised as fic, exploring power imbalances and the terror of being trapped together forever. Sometimes I'll see a premise on Tumblr and think 'oh that's neat,' then six months later someone's turned it into a 50k epic on AO3. The platforms feed each other, honestly. Twitter... eh, it's okay for finding art links and screaming into the void with other fans, but the actual readable content feels more scattered and less curated.