gσ∂∂єѕѕєѕ σƒ ∂єαтн αη∂ тιмє;;
χ…Saturn and Pluto are entwined in their powers, and it is seen (especially in the manga) that they work together. Saturn is the Soldier of Silence (Destruction & Rebirth). Pluto is the Soldier of Change (Revolution). These cannot exist on their own.
Saturn's sole purpose is to “restart” the universe—bringing Silence. Although she destroys, she is able to cause rebirth and is reborn herself. Pluto guards the door of Space-Time in the Underworld. She is born of Chronos but herself is a manifestation of the God Pluto/Hades.
The fact that Setsuna adopts Hotaru as a daughter (along with Michiru and Haruka, of course) can be seen as Hotaru quite literally being the daughter of Hades. Destruction and Rebirth are linked with Death and Time. Setsuna and Hotaru are entwined in more ways than one.
χ… The two are implied to quite literally be goddesses. They are powerful and of all the soldiers, are the two you would not want to make angry with their unique (and burdensome) powers. On their own, Saturn and Pluto can be deadly, but together they are bone-chilling terrifying.
Abilities going hand in hand, they together represent the cycle of life and death.