Michiru Kaiou / Sailor Neptune

Michiru carries over the look of her manga self, though the anime shortens her teal hair to a medium length. At Mugen Academy she wears the school's dark sailor uniform with a checkered bow and skirt, topped by a black headband, and swaps in a summer variant when the weather warms. Off campus she favors elegant layered outfits, often a long jacket over a v-neck shirt, and in the final season she lets her hair fall loose beneath a red short jacket and pink dress.

Her guardian uniform is built on a chest-armored white leotard with teal collar, choker, skirt, and heels, gold planetary earrings, and a green-gemmed tiara. The Super Sailor upgrade lengthens her back bow, adds a green heart to the front, sets a star on her choker, and reshapes her shoulders into translucent wings.

She reads as refined and worldly, carrying herself with an elegance that can tip into coolness, and she is capable of sudden, cutting anger. Above all she is unwavering in her guardian duty, ready to do whatever that mission demands.

In her past life Michiru stood among the Outer Guardians who shielded the Silver Millennium from outside threats, granted greater power for the task. Long before awakening, she became fixated on Haruka and watched her from afar, later learning it fell to her to stop the Silence by finding the true Messiah. When Haruka hesitated to accept a guardian's fate at a racetrack, Neptune threw herself in the path of a Proto-Daimon's blast and was badly hurt; afterward she confessed her feelings, and Haruka joined her. The pair went on to seek the three Talismans hidden in Pure Heart Crystals, enrolling at Mugen to investigate their foes.

Through Sailor Moon Super they turn up at the Death Busters' attacks, testing victims for a Talisman and clashing with the Inner Guardians over whether killing for one is ever justified. Lured to the Marine Cathedral by Eudial, both have their own Talismans, the Deep Aqua Mirror and Space Sword, torn out and are seemingly slain, only for Sailor Pluto's Garnet Orb to revive them and complete the trio that summons the Holy Grail. They come to suspect Hotaru is the Messiah of Silence and argue she should be kept from Chibiusa, even killed. When Pharaoh 90 threatens the world, they surrender their power so Sailor Moon can transform without the Grail, and afterward realize Usagi was the true Messiah, bowing to her budding form as Neo Queen Serenity before driving off.

Reunited with the heroes in Sailor Stars, the two eventually trade their souls to Galaxia to keep living together, stealing the Star Seeds of Pluto and Saturn under her control. Their treachery proves a ploy to seize the strength needed to strike at Galaxia, and when it fails she strips the bracelets keeping them alive. Reaching for each other, Michiru and Haruka fade away together, only to be revived alongside everyone else at the end.