Nanami Takatsuki is Cinque Izumi's older cousin and athletic rival, holding an undefeated record against him in Iron Athletics competitions modeled after Ninja Warrior courses. Residing in London created distance from Cinque, limiting their interactions before her summoning to Flonyard.

Leonmitchelli of the Galette Kingdom summoned Nanami to serve as its heroine, mirroring Cinque's role as the Biscotti Republic's hero. She wields the adaptive Divine Sword Ex Machina, which shifts to her preferred staff form and generates ice skates for enhanced mobility across water. This versatile weapon also manipulates water and transforms into a boomerang with unpredictable trajectories, occasionally catching experienced opponents like Brioche d'Arquien off guard. Nanami collaborated with Cinque to create the combined technique "Internal Neptune: Twin God Fist" during a confrontation with Rebecca Anderson.

Her personality blends enthusiasm for challenges with a competitive spirit and caring attitude towards Cinque, alongside a playful tendency to offer physical affection to allies like Leonmitchelli, which Prince Gaul initially resisted. She embraced her heroic duties in Flonyard with vigor, actively participating in wartime efforts and daily life within Galette and its allied nations.

During Season 3, Nanami received a Spirit Crystal from Adel, enabling a temporary adult transformation that amplified her water and ice-based abilities. Her combat prowess was further demonstrated in an extended near-equal confrontation against Brioche d'Arquien, recognized as Flonyard's strongest fighter, before her eventual defeat.

In the OVA "Limone Resort - Panorama Spa", Nanami appears in a non-canon hot spring setting alongside other characters.