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In a past life, Beryl, who lived on Earth with Prince Endymion, seemed to have profound feelings for him. She had incredible hatred towards Princess Serenity for capturing the heart of Prince Endymion, and that was amplified by being possessed by Queen Metalia. This was what lead her to destroy the Moon Kingdom, and although Endymion died as well as Serenity, she was cruelly delighted. After being reincarnated, Queen Beryl continues the work of the Dark Kingdom and Queen Metalia.
Tuxedo Mask is captured by Kunzite and delivered to Queen Beryl. Beryl brainwashes him to love her and do her bidding. She sends Endymion to Tokyo as "Endo" in order to find the underground command center, figure out the identities of the Sailor Senshi, and kill them. After hypnotizing Makoto, he is lead to the command center and makes an ambush on the Senshi. Beryl appears before him, claiming he is a servant of the Dark Kingdom now. Beryl is killed by Sailor Venus, but Endymion remains evil.
When Beryl sees Tuxedo Mask, she realizes he is Prince Endymion reincarnated. She captures him and corrupts him turning him against Sailor Moon. She wants him to rule alongside her in the Dark Kingdom. She sends Endymion back into Tokyo to attack and kill the Sailor Senshi. Due to the Senshi's efforts against him, Beryl has to rejuvenate the evil in Tuxedo Mask multiple times.
When Sailor Moon is transported to Beryl's lair, she sends Endymion to kill her. Beryl laughs at Sailor Moon's attempts to try and heal him, claiming he will never go back. To her surprise, Tuxedo Mask is eventually freed from Beryl's control, making her angry. Beryl tries to attack Sailor Moon but she is injured by his rose, shocking her and forcing her to retreat. She soon combines with Queen Metalia to become Super Beryl who is later slain by Sailor Moon.
Beryl and Mamoru is an villains ship. In the show and manga, it's always portrayed as one-sided, with Beryl wanting Endymion. Endymion only returns her feelings when he is brainwashed, though because of that, many believe their relationship is superficial. The ship is heavily disliked due to Beryl's manipulation and feeling of entitlement toward Tuxedo Mask. Due to the ship's negative reception, its rival ships, the most notable being MamoUsa, are much more popular.
Fanworks often portray a universe where Beryl wins the love of Mamoru (any incarnation), whether it be by force or naturally. Some theorize about what would have happened between the two had Metalia not possessed the Earth during the Silver Milennium. In these cases, Beryl just has the unfortunate circumstance of pure, unrequited love. Occassionally, an alternate timeline is explored, where Prince Endymion is meant to be Beryl instead of Princess Serentity.
- Beryl brainwashing Tuxedo Mask would start the trend in Sailor Moon of the female villains always manipulating him.