Inside the Dark Crystal, Prince Diamond accuses Wiseman for disobeying a direct order by killing Sapphire. Wiseman says Sapphire was a traitor and that he wants no one to stop their plans to take over the world as revenge for their banishment to Nemesis.
The girls all transform and enter the Dark Crystal. Sailor Moon falls down a trapdoor and enters the room Diamond is in. Diamond tries to hypnotize her into loving him again, but she keeps saying Darien's name instead, and his power does not work on her. Sailor Moon convinces Diamond that Sapphire was telling the truth. When Wiseman appears and tries to convince him otherwise, Diamond refuses to listen to him, and Wiseman says he no longer needs him. Diamond fights him, saying he'll avenge Sapphire and Emerald's deaths, and they enter a beam struggle. Wiseman says he will destroy everything in the name of the Doom Phantom, and then directs an attack of dark spears at Sailor Moon. Diamond jumps in front of her and is impaled by the attack. However, Diamond shoots an energy blast at Wiseman, shattering him to pieces and leaving an empty cloak.
Diamond dies in Sailor Moon's arms, saying he would have liked to find out more about Earth and start over now that he realizes he was wrong. Wiseman pulls himself back together and tries to trick Sailor Moon with illusions of Tuxedo Mask, but she doesn't fall for it. Tuxedo Mask arrives and attacks Wiseman, who goes to the Dark Gate to open it and destroy Earth. Tuxedo Mask knows where the Dark Gate is, and leads the Sailor Scouts to it, at the top of the Dark Crystal, where they encounter Wicked Lady.
- Final appearance of Prince Diamond.