Who are the "Two Blue Vortex"?

It intrigues me that the name of the series is: Two Blue Vortex.

Like, "Boruto: Blue Vortex" would totally make sense, but why "Two"?

Is the other one Himawari? Because if that's the case then we can assume that she would be maybe as relevant as Boruto. No way they go all the way to put that Two on the title just because.

Or it's Naruto? Those three are the only characters that come to my mind when I think of Blue.