Maki Nagashiro begins as the Secretary of Miyaji Academy's Student Council in the anime's third season, rising to Vice President by the fourth. She possesses purple hair, red eyes, and wears glasses. Initially silent and serious, she dedicates herself to duties, often working silently on her computer. This reserved nature shifts dramatically after her transformation.

Her background involves covertly monitoring the Cardfight Club for an unknown entity from a hidden academy room. Discovering Naoki Ishida eavesdropping, she defeats and Reverses him, connecting him to Link Joker. She later orchestrates the Reversing of others, including Kourin Tatsunagi during a school camping trip and Shingo Komoi during a school confrontation. As a Reversed agent, she leads other Reversed students with calm authority, expressing satisfaction in spreading Link Joker's influence.

In conflicts, she employs psychological manipulation, targeting Naoki by highlighting their mutual isolation and promising freedom from pain through Link Joker's power. She wields a Neo Nectar deck featuring Maiden of Venus Trap "Reversed" and Deep Green Lord, Master Wisteria, using abilities to rapidly summon units from the deck for field advantage. Her tactics involve ensnaring opponents in symbolic vines representing isolation.

Her Reversal ends when Naoki Ishida defeats her in a cardfight, breaking Link Joker's control. She collapses and later awakens with no memory of her Reversed actions. Tatewaki Naitou and Itsuki Suwabe reassure her she is no longer alone, signifying her reintegration. By the fourth season finale, she appears at the expanded Cardfight Club, offering encouragement for the upcoming High School tournament and specifically wishing Naoki good luck.

Her surname, Nagashiro, combines "long" or "chief" (長) and "generation" (代). She is the first anime character to be Reversed and the first not Reversed through a cardfight with another Reversed fighter.