Hrm, very well.
Perhaps, say, they both were members of small fighting forces hired for a particular combat, and got seperated from their peers. While looking for their companions they found each other, and, having been from the same side, worked together to find their respective groups, though this caused them to spend a day or more in close contact with each other, they have found that both are relatively proficient, professional indeviduals and have formed a working relationship, with undertones of something more.
Though that does bring about the question, who's steering the world on this?