Cyprin, the fifth and final of the Witches 5, devises a plan to steal Pure Hearts from the students of Mugen School to feed to the Sovereign of Silence. Kaorinite overhears Cyprin say that she would do a much better job than her, so she decides to extract the strongest Pure Heart she knows of: Rini's Pure Heart.
The students appear in a trance as Cyprin summons them to the school. She begins draining their Pure Hearts using a statue of the Sovereign of Silence. Serena, Amy, Raye, Lita, and Mina are teleported to a room as they come to investigate, and they transform and fight her. Sailor Venus traps Cyprin with Venus Love Chain Encircle, but a red energy beam stops her attack. The attacker is another witch named Petirol, who looks like Cyprin except she has red hair. Cyprin shares her mind and body with Petirol. The Sailor Scouts fight Cyprin and Petirol, but they block all of their attacks.
The Sailor Scouts decide that the only way to beat Cyprin and Petirol is to separate them. Sailor Mercury uses Mercury Bubbles Blast, and after a few more attacks (during which Sailor Moon uses Moon Tiara Magic), Sailor Jupiter tackles Cyprin, who chases after her. Sailor Mars knocks Petirol down, and she chases after her. Cyprin shoots a powerful energy wave at Sailor Jupiter just as Petirol is shooting an energy wave at Sailor Mars. Sailor Venus gets Sailor Jupiter out of the way of Cyprin's attack, and Sailor Mars dodges Petirol's attack, causing the witches' attacks to hit each other and destroy them both.
The statue is destroyed and all the Pure Hearts are returned. The Sailor Scouts discover the corridor to have a warped space, and they follow it to lead them to the Heart Snatchers. Sailor Uranus and Sailor Neptune arrive to see Doctor Tomoe and the Sovereign of Silence with Sailor Mini Moon, protected by a forcefield, which electrocutes Sailor Uranus as she tries to run over to stop them. The Sailor Scouts arrive, and Sailor Moon tries to run over to Sailor Mini Moon, but is also electrocuted by the barrier.
The Sovereign of Silence extracts Sailor Mini Moon's Pure Heart and eats it. She then awakens in her true form, as Mistress 9. She sends bolts of lightning flying everywhere. One of them hits Kaorinite, throwing her into the forcefield and killing her. Mistress 9 says she did her job and they don't need her anymore. She then destroys the top of Mugen School. The Sailor Scouts escape, and Luna, Artemis, Sailor Pluto, and Tuxedo Mask get the students out.
Darien uses his power to keep Sailor Mini Moon alive, and Sailor Pluto decides that the only way to stop Mistress 9 is to destroy her, and Hotaru with her.
- First unshadowed appearance of Cyprin
- First and last appearance of Petirol
- Final appearance of Cyprin and Kaorinite
- First true appearance of the Sovereign of Silence as Mistress 9