Mylène, known in other versions as Michiru Kaioh, is the civilian identity of Sailor Neptune in the anime Sailor Moon S: The Movie. She is a member of the outer solar system guardians, a group of warriors tasked with protecting the boundaries of the solar system and defending Earth from threats that come from beyond. In the film, she and her partner have already awakened to their duties and operate independently of the inner guardians, guided by a strong sense of mission and a willingness to make difficult choices for the greater good.

Mylène is introduced as a calm, elegant, and sophisticated teenage girl with a deep passion for the arts, particularly the violin. She is a gifted musician who often performs in public, and her refined demeanor and graceful presence set her apart from the more exuberant inner guardians. Beneath her composed exterior, however, she possesses a sharp intellect and a fierce determination. She is capable of coldness and ruthlessness when the situation demands it, but she is not devoid of warmth; her actions are motivated by a sincere desire to protect the world, even if that means sacrificing her own happiness or the lives of others.

Her primary motivation stems from her role as a guardian of the outer solar system. She believes that the mission to preserve order and prevent catastrophe must take precedence over personal attachments. This pragmatic, almost black-and-white worldview sometimes puts her at odds with the more hopeful and merciful approach of Sailor Moon, but she remains open to growth as she witnesses the power of love and unity.

In the context of Sailor Moon S: The Movie, Mylène and her partner are already active defenders. They investigate the mysterious comet and the threat posed by the Princess Kaguya and her ice minions. Mylène uses her precognitive abilities to sense danger and her tactical mind to plan their moves. She fights alongside her partner, providing support with her water-based attacks and the Deep Aqua Mirror, a talisman that reveals truth and can be used offensively.

The most important relationship in Mylène’s life is with her partner. The two share an inseparable bond, often working as a single unit both in battle and in their daily lives. Their relationship is one of deep trust, mutual understanding, and romantic love, anchored by their shared sense of duty. Mylène’s demeanor softens when she is with her partner, and she is fiercely protective of her. In the movie, this bond is tested by the overwhelming power of the enemy, but ultimately it reinforces their resolve.

Mylène’s character does not undergo a major transformation specifically within the film, but she is part of a broader arc of development across the series. Her encounters with Sailor Moon and the inner guardians gradually challenge her rigid adherence to pragmatism, allowing her to embrace a more compassionate perspective. In the movie, she is already a mature and competent warrior, but she learns to trust in the strength that comes from collaboration rather than isolation.

As Sailor Neptune, Mylène commands powers tied to the sea. Her signature attack, Deep Submerge, creates a powerful torrent of water that she can shape into a concentrated blast. She also wields the Deep Aqua Mirror, which allows her to see into the future, uncover hidden truths, and reflect attacks. Her abilities are enhanced by her keen intuition and strategic mind, making her a formidable opponent who relies on precision rather than brute force. In her transformed state, she embodies the fluidity and depth of the ocean, moving with grace and striking with the force of a tidal wave.