For Friendship: Ami vs. Bertheir

Ami signs up for an international chess event at the Chess Tower, only to learn that Berthier of the Black Moon Clan has marked the building as the next Crystal Point. What begins as a game of skill escalates into a duel where losing the match means dying, and Ami must weigh victory against the lives of her trapped friends.

Berthier, rattled by Koan's recent defection to humanity, volunteers for the mission and starts corrupting the tower with Dark Water. Ami discovers her at work, transforms into Sailor Mercury, and clears the taint with Shine Aqua Illusion, while a surprise strike from Sailor Jupiter forces the enemy to flee. Refusing help from her sisters Petz and Calaveras, Berthier brainwashes a receptionist and enters the tournament to face Mercury directly.

Ami checkmates her opponent, but Berthier seizes the game room, snares the other guardians in a lethal trap, and rigs a rematch, freezing Ami piece by piece as she falls behind. Ami refuses to flee and forsake her friends, a stance Berthier cannot comprehend. Tuxedo Mask shatters the enemy's queen to break the spell. When Petz and Calaveras coldly leave Berthier to die, she snaps and hurls Dark Water Full Power in a bid to kill everyone with her. Koan arrives to reach her sister, and Sailor Moon uses Moon Crystal Power to restore Berthier's humanity.

The story closes with Koan and Berthier playing chess as sisters while Luna, Ami, and Usagi look on. In the manga, Berthier met a far darker end, killed by Moon Princess Halation just as Koan was. Viz Media renders her name as Bertheir in the episode's title. Several dubs softened the material: DiC erased the blood drawn when Jupiter's attack struck Berthier and reworked the sisters' talk of preferring death to becoming human. This entry also introduced a new opening depicting Crystal Tokyo.