Izumi Nana, identified as Joanna in the Filipino English dub, serves as a central narrative figure. She possesses short blonde curly hair tied with red ribbons on both sides, pale pinkish skin, large blue eyes, and a notably short stature, typically dressed in a blue shirt and shorts.

Raised by her grandfather Shinchiro Izumi after her parents' unexplained absence, she grew up alongside adoptive brother Kazuya Ryuzaki following his father's death. Both underwent karate and piloting training under Shinchiro, with Nana specializing as a gunslinger while Kazuya focused on astronautics.

Nana displays a childlike, innocent, and upbeat personality but reacts with quick anger to perceived disrespect. She initially disliked Reiko for bratty behavior, requiring restraint by Kazuya to prevent fights. Conversely, she often restrains Kazuya during his outbursts, such as when Kyoshiro accused Erika. She champions justice, openly criticizing General Miwa for unfair treatment of Kazuya.

Though initially upset discovering Kazuya's romantic feelings for Erika, Nana accepted their relationship upon seeing it brought him happiness. She actively supported Kazuya's missions to reunite with Erika. An excellent markswoman and occasional co-pilot of the Galva FX-II combat plane, she fought alongside Kazuya and Kyoshiro.

Nana temporarily departed after a critical mistake nearly cost her life, returning with a more serious demeanor. Her caretaker, Okane, and Okane's nephew Genta feature in her personal life, particularly later. She intervened decisively when General Miwa attacked wounded Baam refugees, joining Kyoshiro to physically restrain Kazuya from violent retaliation against Miwa.

Throughout the conflict, Nana maintained her belief in Erika's inherent goodness despite her Baam heritage, upholding moral principles above wartime prejudice. Her role evolved from a jealous sibling figure to a disciplined supporter of peace between Earth and the Baam people.