I'd say one of my favorites is a "slow discovery" fic. So often in ship stories one or both of the characters are instantly attracted (even in enemies to lovers stories) and then there's just a lot of denial or secret pining. I'd say it's a little different from a slow burn in that the pair isn't just unaware of an attraction, there just isn't one at first, and what's more their eventual relationship is not the center point of the fic either. Instead it's a story where that becomes a piece of it.