Nanami is the stepsister of the protagonist Riliu and the adopted daughter of Genkaku. Growing up in the town of Kyaro in the Highland Kingdom, she spent most of her childhood playing with Riliu and their friend Jowy, and the three of them were somewhat isolated from other children as a result. She is known for her bright and cheerful demeanor, always wearing a smile and maintaining an upbeat and energetic attitude, though she can sometimes be overly assertive or overbearing in her care for others. During the time Riliu serves in the Unicorn Youth Brigade, she takes charge of the household.

Her primary motivation is her deep, protective love for her brother. She does not want to see him suffer in the war and repeatedly tries to convince him to abandon the fight and run away. Over time, she comes to respect his decision to continue leading the Unification Army, but the conflict causes her great inner pain, especially because it forces Riliu to fight against their childhood friend Jowy. Her role in the story is that of a steadfast companion and protector who remains by Riliu's side for much of the journey. Her key relationships are with Riliu, whom she watches over with fierce devotion, and Jowy, whose divergence from their shared past deeply wounds her. A small flying squirrel named Mukumuku also keeps her company while Riliu is away.

Nanami undergoes significant development as she grapples with the harsh realities of war. Her initial impulse to flee is eventually tempered by acceptance, though she remains privately hurt. During the siege on Rockaxe, she is severely injured by an arrow in what is initially believed to be a fatal wound. It is later revealed that she staged this as a way to remove herself from the war, unable to bear watching her brother suffer or fighting against Jowy. She stays in Kyaro until the conflict ends and afterward travels together with Riliu and Jowy. In combat, Nanami is an adept user of the three-piece-rod, and her agility in battle is rarely matched.