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Depends on the story and setting. Have them advise each other on romantic problems. Make her older or more mature than he is, which creates a gap that can close during the series. (You could try it...
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#2: Initial revision
Depends on the story and setting. Have them advise each other on romantic problems. Make her older or more mature than he is, which creates a gap that can close during the series. (You could try it the other way around, but sweet young thing and worldy wise older guy is still a trope, albeit an out of date one).