Marine is one of the three main protagonists in the anime Magic Knight Rayearth 2, and she is the Magic Knight who commands the power of water. She is a fourteen-year-old eighth-grade student from a wealthy family and is an only child, attending a private school where she is the captain of the fencing team. Marine has long blue hair and blue eyes, and she stands as the tallest of the three Magic Knights. When first introduced, she gives the impression of being self-centered and quick to complain, often reacting with irritation to the strange events that pull her and her friends into the world of Cephiro. She has a short temper and speaks her mind without hesitation, which initially makes her seem snobbish or overly critical. Beneath this exterior, however, she is deeply loyal and protective toward her fellow knights, Hikaru and Fuu, whom she treats like younger sisters. Marine is also highly sensitive and can become emotional when her friends are in danger, gradually revealing a generous and caring nature as the story progresses.

Her motivations in the first season are primarily to return home to her normal life in Tokyo, but she grows increasingly invested in the fate of Cephiro and its people. In the second season, set one year after the events of the original series, Marine is initially burdened by guilt over the death of Princess Emeraude, but she returns to Cephiro to help defend it from external threats. She becomes more mature and controlled in battle, showing less impulsiveness and a stronger sense of responsibility. Her role in the story is that of the water-element warrior, often using her fencing skills and magical spells to protect the castle and its inhabitants from invaders from the worlds of Autozam, Fahren, and Chizeta.

Marine wields a rapier forged from the rare mineral Escudo, which melts if anyone other than her touches it. Her magical abilities include Water Dragon, a spell that summons a serpent of water; Ice Blade, which creates a frozen sword or projectile; and Blue Tornado, a powerful vortex. Her Rune-God, or Mashin, is named Selece, a blue dragon-like being that she pilots in combat. Marine also has a notable rivalry with the creature Mokona, often losing her patience with its playful behavior, though she eventually develops a fondness for it.

In terms of key relationships, Marine forms a close bond with Hikaru and Fuu, and the three of them support each other through the trials of both seasons. She has a romantic interest in the mage Clef during the anime storyline, though he regards her only as a friend. The young mage Ascot harbors strong feelings for her, and while Marine does not reciprocate them in the same way, she values his friendship and treats him with kindness, especially as he matures between the first and second seasons. Marine’s development is one of the most noticeable among the trio: she starts as a privileged and hot-headed girl but grows into a compassionate, determined, and reliable warrior who learns to put the needs of others ahead of her own frustrations.