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It is possible that the writers originally intended to pair up B'Elanna Torres and Chakotay. Of course, Star Trek rarely pairs up couples on purpose--it is not the intent of the show. (Phil Farrand has some snarky things to say about how many Trek characters are lacking in even basic social structures: X-Files Mulder and Scully run amuck.)
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B'Elanna is ambitious and gifted. She left Starfleet because she felt like an outsider. While there, she argued constantly with her instructors (she learns later that many of them respected her and hoped she would return). She is afraid of her own temper, her Klingon half, and has to learn to perceive it not as a barrier to her goals but a source of strength.
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While B'Elanna is ultimately a leader (and prefers a team), Paris is ultimately an iconoclast: pilot, astronaut, racer. They work well together because their personal competitiveness doesn't run up against each other--they aren't competitive about the same things.
Even their senses of humor match up. While Tom Paris is a popular culture buff, enjoying spoofs and satires and prat falls, B'Elanna is dryly ironic. She watches silly television with him because it makes him happy. And he doesn't expect anything from her but what she can and will give.
Well-written and well-scripted! And the actors enjoyed themselves too.