Star Trek: 10 Reasons With Sisko & Kira's Relationship Is Key To Deep Space Nine
6. Evolving Relationship
Outside of their professional relationship, Kira and Sisko had a personal relationship that was always evolving. It would be trite to describe it as a "father/daughter" dynamic. It would be even less accurate to use the phrase "sexual tension" to depict their relationship. But it was still a deeper relationship than even "friendship" could describe.
Their relationship sure didn't start out that way. In the beginning, Kira just saw Sisko as another authority figure to rebel against. Sisko knew he needed a Bajoran First Officer but he wasn't prepared for the level of stubbornness, and sometimes outright hostility, he got from Kira in the early days.
But as time went on, a genuine respect and friendship grew, mirroring the growth in the relationship between Bajor and the Federation. It's unlikely that any other Starfleet officer took a major in the Bajoran Militia to a holodeck baseball game, though.