Berthier (called Bertie in English dubs, sometimes Birdy) is the second-youngest of the four sisters—or the youngest depending on the version. Her name comes from the mineral berthierite and is pronounced roughly "BEAR-tyay." She wields the attack "Dark Water" and serves as a counterpart to Ami Mizuno.
In the manga, Berthier is tasked with killing the Sailor Senshi and capturing Chibiusa. She poses as a human dowser, using a pendulum to impress people, until she spots Ami locating a pipe leak without one—instantly revealing her as a Senshi. Berthier's a skilled chess player and challenges Ami to a televised match, where she openly taunts her as "Sailor Mercury" and tries to use the Black Crystal to trap her. When fighting breaks out, Berthier proves strong enough to deflect Mercury's Shine Snow Illusion. She eventually uses sewage water to choke Mercury, enabling Rubeus to kidnap her before Sailor Moon kills Berthier.
In the anime, Berthier's a darkly playful character who genuinely loves her sisters—she's notably the only one devastated when Cooan gets purified. Like Ami, she's a natural strategist and chess master, though not above cheating. During a final chess match with Mercury, her freezing plan crumbles when Petz and Calaveras show up claiming they'll take the credit anyway. The distraction costs her; Tuxedo Mask rescues the Senshi, and her sisters abandon her as a failure. Desperate and heartbroken, Berthier attempts a suicide attack using all her power in one massive blizzard. But Cooan, newly healed, reaches her—reminding her she's still loved and deserves another chance. Berthier accepts Sailor Moon's healing instead. Eventually, she and Cooan convince their two older sisters to leave their dark path and become human.
Content compiled by AnimeList.moe from publicly available sources.
