At the end of "Sailor Moon Eternal," the Sailor Guardians are able to overcome the nightmares and take down Nehelenia, destroying her mirror realm and reversing the damage done to the planet. But aside from that, the characters undergo a very important transformation in the final act that makes them more powerful than ever before.
In the big face off with Nehelenia, Sailor Moon, a.k.a. Usagi, and the Sailor Guardians go through a final transformation into the "Eternalized" version of themselves. Becoming Eternal Sailor Moon, Usagi gains enough power to completely destroy Nehelenia and all of her creations. The Eternal form of the Sailor Guardians is their strongest state, giving them enough power to destroy entire realms, and it's rarely ever shown in the anime. Thankfully, "Sailor Moon Eternal" gives the Guardians a huge power up worthy of the movie event.
On top of that, the final moments of "Sailor Moon Eternal" show Usagi and Mamoru transforming into Neo Queen Serenity and King Endymion, no longer prince and princess, which leads Luna to exclaim in surprise that they are her king and queen and this is basically their coronation. It looks like the couple understands their responsibility as the rulers of both the Earth Kingdom and the Moon Kingdom, and they are dedicated and eager to keep their people safe. The Sailor Guardians — and Tuxedo Mask — are then sent back to Earth, but is this the end of the story?
