Nanami Takatsuki is a character introduced in the later part of the first season of the series and becomes a more prominent figure in the second season. She is the older cousin of the main protagonist, Cinque Izumi, being two years his senior. Of mixed British and Japanese descent, she lives in London and is a high school student. She is also an acquaintance of their mutual friend Rebecca Anderson. From her first appearance, Nanami is established as an exceptionally athletic and competitive individual. On Earth, she is Cinque's rival in a sport called Iron Athletics, a demanding obstacle-course competition that closely resembles the real-world Ninja Warrior challenge. She holds the top ranking in this competition, a fact that Cinque, who placed second, keenly feels.

Nanami's personality is defined by her energetic and enthusiastic nature. She approaches everything with full commitment and an innocent, straightforward attitude. When faced with difficult challenges, she becomes intensely focused and serious, giving her absolute best effort. This dedicated mindset, combined with her natural physical talent, makes her a formidable competitor and a reliable ally. She genuinely enjoys the thrill of a good challenge, and her rivalry with Cinque is a source of friendly but intense motivation for both of them.

Her role in the story begins when she is summoned from Earth to the magical world of Flonyard by Princess Leonmitchelli of the Galette Lion Dominion. This mirrors Cinque's own summoning by Princess Millhiore of the Biscotti Republic. In response to Leonmitchelli's request, Nanami agrees to serve as Galette's heroine. As her nation's champion, she is given a powerful artifact, the Ex Machina, which is the counterpart to Cinque's Palladion. She uses this blade primarily in the form of a combat rod, a weapon style befitting her background in staff arts, for which she is also Cinque's teacher.

As Galette's chosen figure, Nanami plays a crucial role in the second season's conflicts. Her abilities are centered on her supreme athleticism and her quick mastery of the magical seals, the powerful signature attacks of Flonyard. She quickly learns to use her own seal cannon, known as the Hail King Water Array Palm, which projects a forceful stream of water from her hand. She can also channel this power into special skates that allow her to move across the surface of water at high speed, granting her exceptional mobility in battle. Her capability is such that she can fight on equal footing with Cinque, who has more experience as a Flonyard hero.

In her key relationships, Nanami's bond with Cinque is layered. She is his older cousin, his teacher in staff arts, and his long-time rival. This dynamic is built on mutual respect and a shared passion for physical competition. Her relationship with Leonmitchelli is one of trust and alliance, as she is the ruler who chose her and granted her the Ex Machina. While she interacts with other characters, her primary relationship in the story is defined by this rivalry and partnership with Cinque. Over the course of the series, Nanami's development is shown through her growing familiarity with the world of Flonyard and her increased mastery of its combat systems, but her core identity as a dedicated, happy-go-lucky, and fiercely competitive athlete remains consistent. She has a notably low sense of modesty in chaotic situations, often taking the destruction of her armor in stride, which highlights her carefree and resilient personality.