I think somewhat similar to Shakky and Rayleigh whenever Tsuru actually retires Sengoku and Tsuru are going to get together.

They entered the marines at the same time 56 years ago along with Garp. [Smoker and Hina seemed to have been trained in the same class, and we see what that did for their interactions. I think there are hints of something there.] Furthermore, Sengoku out of all the marines chose to come with Tsuru to Dressrosa. [Of course he was coming to Dressrosa regardless being that it was related to the Rosinante matter. But, as opposed to with the other marines Sengoku arrived with Tsuru.]

There is of course their interactions where Sengoku mildly annoys Tsuru in a somewhat endearing manner.

Also, according the wiki when Sengoku was an admiral he ordered Tsuru to stop the Doflamingo prates, he was overseeing her. And according to her Vivre Card she served as Sengoku's personal assistant and aide [presumably when he was a Fleet Admiral I'm guessing].

Lastly, they are pretty similar, both of them are very much the strategic side of battle, and level-headed people. They also seem to emphasize duty as we saw with during Ace's execution. I think they suit each other well.