If you're hunting down fic for those two specifically crossing over, your usual bookmarks like AO3 can be hit or miss. I spent ages trying to find something decent and most of what's out there is either super short drabbles or wildly OOC.
A trick I've had luck with is searching the tag for 'Bungou Stray Dogs' or 'BSD' and then filtering by both character names, rather than looking for a dedicated crossover tag. Sometimes writers don't tag it as such, but the story itself is a full crossover scenario. I found a pretty solid one last week that way, where Tecchou gets transported into Jouno's timeline and they have to work together—it was tense and weirdly funny.
Honestly, the scarcity makes finding a good one feel like a victory. Makes me wish more people would play in that sandbox.
Jouno and Tecchou's dynamic is built on the sandcastle of mutual misunderstanding, which is why fanfic writers love to watch it crumble. He can't see, and he won't listen; she's all blunt force where he needs subtlety. Their conflicts don't come from hating each other's guts, but from wanting the same things—safety, validation, a place to belong—and being constitutionally incapable of asking for it in a language the other understands.
That's where the good stuff happens. It's Jouno provoking a reaction because feeling Tecchou's anger is more real than his silence. It's Tecchou following orders to the letter, a form of devotion that looks like indifference, leaving Jouno scrambling for any scrap of genuine emotion. The real tension isn't about them fighting the world, it's about them fighting their own instincts to reach across that gap. I've read fics where they're stranded together and bicker for 10k words over how to build a fire, and it's more charged than any outright confession.
Truthfully, I think the best tension for Jouno and Tecchou comes from scenarios that force them into roles opposite their comfort zones. Jouno being the vulnerable one while Tecchou has to navigate a situation with his blunt honesty is a goldmine. I read one where an injury left Jouno temporarily dependent on him, and the tension wasn't just physical proximity—it was the quiet, simmering frustration of Jouno not being able to use his usual methods of control, and Tecchou's straightforward care accidentally dismantling Jouno's walls.
That dynamic of enforced closeness with unresolved professional rivalry is everything. The real spark happens in the quiet moments after the action, when the adrenaline fades and all that's left is the awkward reality of their partnership. Tecchou trying to interpret Jouno's silences, Jouno analyzing every shift in Tecchou's tone—that's the good stuff. It's less about grand declarations and more about two people who communicate in entirely different languages being stuck in a tiny, high-stakes space.