The best-selling shōjo manga, Sailor Moon, is known for its Sailor Guardian heroines. However, there are more Sailor Guardians than many people may realize, and not all of them are heroes. Some of them even went to the dark side. One in particular is one of Sailor Moon's greatest foes - and technically, Sailor Moon didn't defeat her, even by the manga's standards.
Sailor Moon began publication in 1991, serialized within Nakayoshi, a shōjo manga magazine published monthly by Kodansha. Created by Naoko Takeuchi, this magical girl story features the titular heroine Sailor Moon facing evils within the galaxy as she rebuilds and protects her kingdom. Sailor Moon fights with the power of love, hope, and friendship, which are all things her enemies continuously attack.
In the last arc of the series, known as the Stars arc, Sailor Moon has to face off against a foe named Galaxia. Galaxia was once a Sailor Guardian who was supposed to protect the universe, just like Sailor Moon and her Inner Senshi (Mercury, Mars, Venus, and Jupiter). However, her home planet was a place of destruction. Disappointed by her place of origin, she left to seek out a better planet to call home. This Sailor Moon villain's quest turned into one for power, as she wanted to live on the strongest star. She set her eyes on a place in the center of the galaxy - Sagittarius Zero Star - the place stars are born.
Galaxia is the leader of the Shadow Galactica and to achieve her goal of ruling Sagittarius Zero Star, she seeks to raise her power. Each Sailor Guardian has the abilities they do because of Sailor Crystals, so Galaxia and her underlings seek out other Sailor Guardians and kill them, stealing their Sailor Crystals. This leads her to raise her power immensely - enough to rival Sailor Moon. Despite being about the same power level in terms of potential, Galaxia becomes the stronger of the two physically. Yet as fans know, Sailor Moon's strength doesn't come from her physical abilities - it comes from her hope, trust, and love, which is often bolstered by her friends and her love, Tuxedo Mask.
Unfortunately for Sailor Moon, Galaxia is aware of this and purposely forces the titular heroine to fight - and kill - her friends' reanimated bodies. However, at the moment Galaxia offers Sailor Moon as a sacrifice to Chaos in exchange for power, she also sees the truth about how she is perceived by Chaos itself. The two are left unable to continue fighting, losing their willpower to do so. Seeing the strength of Sailor Moon firsthand makes Galaxia realize that Sailor Moon's the star she has been looking for and the power was never actually hers to attain. This causes her to lose her only purpose and be destroyed by the shattering of her bracelets.
While Sailor Moon technically defeated Galaxia by revealing the truth, Galaxia's power never lowered or emptied. Her crystal's power rivaled Sailor Moon's and the only thing that ended this battle was a moment of self-reflection and realization. Galaxia's demise means that Sailor Moon reigns as the most powerful Sailor Guardian in the end as a technicality, because in terms of ability, Sailor Moon never truly defeated her rival in a contest of strength. The fact that Galaxia could hold her own against Eternal Sailor Moon is already a testament to her power and skill. The villains in Sailor Moon pack the biggest punches, but Sailor Moon's greatest strength is her ability to fight with a style that is all her own and outlast their evil goals with her hope.