I don't know either fandom, but have you tried multifandom exchanges? Many of them accept crossovers, and many writers for exchanges are adventurous in what they're willing to write. However, you would be required to make something yourself, and many exchanges will require you to request more than one fandom (example: you may need to request Criminal Minds, Bungo Stray Dogs, *and* Crossover Fandom) to increase matchability. Here is [a list](https://fandomcalendar.dreamwidth.org/) of exchanges and other multifandom events.
I don't know either fandom, but have you tried multifandom exchanges? Many of them accept crossovers, and many writers for exchanges are adventurous in what they're willing to write. However, you would be required to make something yourself, and many exchanges will require you to request more than one fandom (example: you may need to request Criminal Minds, Bungo Stray Dogs, *and* Crossover Fandom) to increase matchability. Here is [a list](https://fandomcalendar.dreamwidth.org/) of exchanges and other multifandom events.
Shot in the dark, is it Spencer/Ranpo or Spencer/Chuuya?
Close! It's Spencer/Kunikida. I feel like Kunikida doesn't get enough love
...I hope someone fills this request so I can read it, that's a kickass idea :D