So there's these two characters in a story that you like, and think should totally be together. But you don't think they would ever be romantically involved - just that they would be really really great friends. So you're shipping them together, but not in a romantic-type way....
is the super-trope - or perhaps sister trope - to this, but that's about fans romantically pairing characters together. This is where you just wish they'd be bestest friends. Canonical best-friends come under other tropes, such as BF Fs
, Platonic Life Partners
or Heterosexual Life-Partners