Perhaps their values play a crucial role in the story. If they were both very religious, for example, their faith could have guided their decisions and actions throughout their lives. It might also be that they had a unique experience that set them apart, like being part of a historical event in their town. This could have had a profound impact on who they are and what their story is all about.
I don't know the story, so I can't say for sure. It could be things like their family background as a key element.
Well, if it's a story about their relationship, then the key elements might be their first encounter, the development of their feelings for each other, and any major events that strengthened or tested their bond. For instance, if they faced financial difficulties early in their relationship but managed to get through it together, that could be a key element. Another possibility is that they had a shared passion or hobby that was central to their story, like they both loved painting and it brought them closer in some way.