Full Name: Princess Serenity
Sailor Designation: Princess Sailor Moon
Weapons: Princess Sword/Princess Harp, Ginzuishou
Attacks: Princess Star Attack, Princess Harp Healing

Princess Sailor Moon is a powerful combination of Sailor Moon and Princess Serenity, introduced when Usagi is 'possessed' by the spirit of her former self. She originally appears after Queen Beryl takes the Shitennou hostage in exchange for Mamoru. Silently furious, Sailor Moon transforms into Princess Sailor Moon and halts Queen Beryl using her sword. Her sole intent was to get Endymion back, and she did not shy away from anything in order to achieve her goal. Although Serenity tends to be grouped in with the enemies, she isn't evil, just egocentric and absolute. It is obvious that Princess Sailor Moon is not the same as Usagi when she shows no remorse for the fate of Nephrite, and when she refers to Mamoru as 'Endymion' rather than by Mamoru.

Serenity was the major cause for destroying the world planet in the past, and her powers increased Metalia's strength in the present. She inhabited her reincarnated form of Usagi whenever Usagi became too distressed over Mamoru or was unconscious. Serenity's only concern was Endymion, her forbidden love, and that is what made her dangerous to the planet. In Act 41, Usagi's friend Naru accidentally gets too close and winds up in the hospital for a while. Princess Sailor Moon states to Usagi during inner dialogue that she has no qualms about destroying the Earth if Endymion is ever taken from her. Usagi struggles to suppress her power in fear that she would eventually destroy the world. When Metalia took over Endymion, Usagi had no choice but to kill him. In the Final Act, Queen Beryl demanded to know why the Princess had to take everything away from her, calling her the only evil. Makoto angrily says that Sailor Moon saved the planet from Queen Metalia, but Beryl points out that she also killed Endymion. This makes Usagi realize the magnitude of what she has done and as she yells Endymion's name, a surge of golden light transforms Usagi into Princess Sailor Moon. The Princess declares that she will destroy the planet along with Endymion. Princess Sailor Moon even summons her own special grunts to fight the other Senshi, all bearing moon-shaped signs similar to hers. Ami lead the attack against the grunts, but Princess Sailor Moon released a wave of total destruction from the power of the Ginzuishou. Princess Sailor Moon appeared to Usagi and told her that as long as her friends remember her, she can live.

Princess Sailor Moon has a sword, which also doubles as a harp with invisible strings. She plays this in sorrow while thinking of her lost prince, and is capable of using it to heal people and the land. The harp also feeds Queen Metalia with the power of the Ginzuishou, accelerating the devastation of the planet. Using the sword in its capacity as a weapon, Princess Sailor Moon can deflect enemy attacks and can unleash devastating projectile attacks such as the Princess Star Attack.