A small crystal falls from the sky and is caught by a man outside a space research center.
Michiru, Setsuna and Haruka are getting ready when Michiru notices a shooting star in her mirror. But, they forget about it in their hurry to get to the party. They arrive at the Crown shortly afterwards at attend Mina and Lita's birthday party. Luna and Artemis arrive even later, arguing about Artemis always having to go to Bunny's to pick up Luna and never the other way around. Rini notices an early snowfall. Somewhere a veiled woman cackles.
A later day, Luna sets out to visit Artemis at Mina's house for the first time, even though the route involves her crossing a large road which she balks at. While there, she spotted by some kids who put bandages over her crescent spot. With the spot covered, Luna cannot speak and is dizzy and drained, stumbling into the street as a car comes. She is rescued by the man who caught the crystal, Kakeru Ohzora. He takes care of her and removes the bandages, before his childhood friend, Himeko Nayotake, arrives. They are both astronauts; Himeko waiting to become a pilot for the next space flight, and Kakeru having just discovered a comet he named Snow Princess Kaguya that his crystal is from. Dr Ohzora is called to an emergency meeting, where Luna follows and finds out the comet is heading directly to crash into the Earth. She reports back to the Sailor Soldiers. Michiru uses her mirror and sees the comet fading-- probably burned up.
Luna goes back to return the handkerchief Kakeru bandaged her leg with. He guesses (with some help) her name and ties a yellow ribbon around her neck. The crystal he caught is in a dish, growing larger. Before she leaves, he has dizziness and a shooting pain in his chest.
As the days go by, Luna continues to visit Kakeru, and the others wonder about her. Artemis know it isn't him she is sneaking off to see. One evening Luna asks Bunny what a kiss tastes like, and the girl stammers that it's sweet. As Kakeru's health gets worse, Luna spends more time at his side, realizing she is falling in love.
Kakeru takes vacation time and follows Himeko to the Kennedy Space Center, and Luna follows him. He remembers his childhood pact with Himeko to both become astronauts and find Princess Kaguya on the moon. But then he collapses. At the hospital, Luna and Himeko find out he has a heart disorder, which means he can never go into space.
When Luna returns the other note her continued strange behavior. They deduce she is in love, and it cannot be Artemis. They all talk about how nobody wants to be lonely for Christmas and decide to throw a holiday party.
Kakeru stops by his lab and notices the crystal has grown more and appears to have the figure of a woman in it. He has another attack and collapses.
At the hospital, a woman comes into Kakeru's window saying she is Princess Kaguya because that is what he named her. A nurse enters and Kaguya encloses her in crystal. Luna peeks in and thinks Kaguya is an enemy and goes to get Bunny.
Luna comes back with Sailor Moon who attacks Kaguya. The enemy is unprepared and retreats. Sailor Moon and Luna talk with Himeko when she arrives, deducing the alien crystal of Kakeru's is behind the attack and an invader must be on the comet. Uranus, Neptune and Pluto find the comet was not destroyed, and attempt to take on Kaguya but fail.
As the Sailor Soldiers try to come up with a plan to protect the planet, Himeko is added to the crew of the upcoming Christmas Eve space mission. She goes to Kakeru and swears she will come back to heal him and take him into space with her the next time. As they embrace, Luna enters and sees that it is not her Kakeru loves, but Himeko. She runs off, wishing she were a human girl.
After Himeko leaves for America, Kaguya sends her Snow Dancers to cover the people of Tokyo in crystal. Then, she goes to Kakeru to him as her own, bt the Sailor Soldiers arrive. Kaguya explains that over 4 million years ago the solar system was just forming and she was tossed from it, traveling as a comet, and has returned to take over the Earth. They fight her and the Snow Dancers, driving them back into outer space and following them there. With the power of the Silver Imperium Crystal, Super Sailor Moon destroys Kaguya and the comet.
As Himeko's flight takes off, Kakeru starts feeling better, and Luna still stays at his side. The Sailor Soldiers return to the hospital and know who Luna loves. Using the power of the Crystal, Super Sailor Moon turns Luna into a human as a Christmas present.
Human Luna wakes Kakeru, who thinks she is Princess Kaguya of the Japanese legend. Luna takes him into space and tells him she knows he must live and be with Himeko. He notices her crescent mark and the yellow ribbon around her neck, but Luna silences him with a kiss. Then, she claims to actually be Kaguya and makes him promise to come to the moon to find her again.
Luna returns to Bunny's house where she finds Artemis has been waiting for her on the doorstep all night. They go inside to get ready for the Christmas party. . .
