Kusuke X Kusuo Romane & Geschichten

Honestly I'm not even that deep into the Saiki K fandom anymore but this pairing always stuck with me because of how weirdly intense it gets. It’s not your typical sibling rivalry fanfiction where they're just fighting over parental attention or grades—though that's there too, obviously. The best ones latch onto the canon premise: Kusuo has these god-like psychic powers but he just wants a normal, quiet life, and Kusuke, the 'ordinary' genius brother, is utterly obsessed with surpassing him. Fanfiction writers take that nuclear-level insecurity and run with it. You get these darkly comedic flicks where Kusuke's experiments to measure or outdo his brother escalate into absurd, sci-fi level scenarios that somehow still feel emotionally raw. I read one where he builds a machine to simulate psychic empathy just to understand Kusuo's perspective, and it backfired spectacularly, leaving him overwhelmed by the sensory input of an entire city. It wasn't about winning anymore; it was about this pathetic, desperate need to bridge a gap he could never actually cross. That stuff hits harder than any straightforward confrontation.

Sometimes the rivalry gets twisted into something almost romantic in its single-minded devotion, which I know squicks some people out, but I think that's missing the point. It's less about romance and more about exploring a dynamic where one person defines their entire existence in relation to the other. Kusuke's identity is built around being the 'lesser' brother, and his 'rivalry' is the only relationship he knows how to have with Kusuo. The fanfiction that clicks for me digs into that tragic layer—here's this genius who could have done anything, but he's forever orbiting his brother's sun, burning up with resentment and fascination. It's a rivalry that consumes him entirely, and Kusuo's mostly just annoyed by it, which adds another layer of pathos. You end up feeling sorry for Kusuke even as you're horrified by his actions.

It's interesting you ask this, because honestly? I see way less of it than you'd think given the dynamic. When I do stumble across a fic tagged for them, it's almost always framed through this weirdly academic rivalry lens. Like, they're constantly trying to outsmart each other with inventions or psychic loopholes, but it's devoid of the actual petty annoyance from the show. They write Kusuke like a cold, calculating genius rival instead of the obsessive, emotionally messy weirdo he is. The tension becomes all about intellect, not about that specific, raw need for acknowledgment from his brother that defines him.

I guess the most common trope I've seen is the 'Forced Proximity' scenario—trapped in a lab together during a power surge, stranded on a deserted island after one of Kusuke's experiments goes wrong. It sets up a situation where they have to rely on each other, which can be fun, but often slips into OOC territory where Kusuo starts monologuing about his feelings. The other big one is 'Role Reversal' or 'Power Swap' AUs, where Kusuke is the psychic and Kusuo is the inventor. Those can be clever explorations of their core motivations, but again, they sometimes sand down the abrasive edges that make their relationship so compelling to begin with.

Oh, I've been living in that tag for ages now. The sibling rivalry dynamic is just so... fertile ground, but writers tend to cluster around a few clear tropes.

By far the most common is the 'protective older brother' angle. Even though Kusuke's motives are messed up, a lot of fics soften him post-canon, imagining scenarios where some external threat targets Kusuo and Kusuke goes full-on 'only I get to torment him' mode. It's surprisingly sweet, in a dysfunctional way. They'll have him inventing things to secretly safeguard Kusuo, which often leads to awkward, non-verbal 'thank you' moments that feel true to the characters.

Then there's the alternate universe stuff, where they aren't related. Coffee shop AUs are weirdly prevalent—Kusuke as the genius barista who's obsessed with figuring out the regular who never speaks but always gets the perfect order. High school rivals is another big one, with Kusuke trying to crack the mystery of the top student who shows zero effort. It strips away the familial obligation and just lets their competitive intellect bounce off each other.

A smaller, darker niche explores psychological horror, leaning into Kusuke's canon obsession. Stories where his 'research' crosses even more unethical lines, and Kusuo has to deal with a brother who sees him as the ultimate puzzle to solve, not a person. Those can be tough reads but are often brilliantly tense.

Honestly, the best ones mix the comedy and the creepiness, just like the source material. A fic that has them battling over the last pudding while Kusuke has secretly booby-trapped the kitchen is peak them.