Define the specific trait one character has that the other subconsciously needs (e.g., a chaotic character needs the grounding of a stoic partner).
A misunderstanding or an external force threatens to pull them apart (the "All Is Lost" moment). @Barbarasexappel_Threesome_Ruben_Anny_&_Ashley_...
The first meeting or a shift in a pre-existing friendship. Define the specific trait one character has that