Sailor Pluto, Sailor Uranus, Sailor Neptun and Sailor Saturn
The relationship that Usagi has with them sometimes is a strange one we could say. From the four of them it seems that Haruka is the one who has the most close relationship to her, even when they only just met, Uranus seemed drawn to her and wanting to tell her what’s really going on.
The actual relationship with them is the far protectors, they are from the four planets that are the farest from the sun, and near to the end of the solar sistem and their job is to protect the princess from far (their job is to not let enemies enter from outer space), they had to witness the death of her in the past, and finally got reincarnated on earth along the others. And because they were always protecting from the far, they at the beginning didn’t know how to act around, till the moment when Usagi in desperation during the combat with the enemies wished for them to be united in hearts.
They all care deeply for their princess and want her to stay safe, and the
same is what Usagi trusts them and deeply feels about them, they are her friends,
and when someone is her friend that means that she would try to give to world