Movie
Description
Ain serves as the vice-admiral and second-in-command of the Neo Marines, a position she holds as a trusted subordinate of the organization's leader, Zephyr. Her background is rooted in her time as a promising recruit in the official Marines, where she was personally trained by Zephyr when he was an instructor. She was one of the few survivors of a devastating pirate attack on a Marine training ship that resulted in the death of many of her fellow recruits and cost Zephyr his arm. Years later, when the pirate responsible for this atrocity was granted the title of Warlord of the Sea, Zephyr left the Marines in outrage. Demonstrating absolute loyalty, Ain resigned her commission as well to follow her mentor, becoming a founding member of the Neo Marines, a rogue faction dedicated to Zephyr's vision of eradicating all pirates.

In terms of personality, Ain is characterized by her strict, serious, and disciplined demeanor. She rarely displays overt emotions, maintaining a composed and professional exterior even in high-pressure situations. However, this stoic facade conceals a deep well of devotion and concern for her teacher, Zephyr, whom she unfailingly addresses as Z-sensei. Her loyalty is so profound that she is willing to sacrifice her life for his cause. Despite her dedication, she has been shown to possess a sense of responsibility, taking the blame for her subordinates' failures and showing a flicker of hesitation about the radical path the Neo Marines have taken. While she supports Zephyr's grand plans despite the enormous risks, her emotional core is most visible when her mentor is in danger, culminating in an uncharacteristic display of tears following his death.

Ain's primary motivation throughout the story is to facilitate Zephyr's ultimate goal of destroying the three End Points, which would unleash a cataclysm upon the New World. She acts as his most capable operative, overseeing Neo Marine operations and directly engaging the Straw Hat Pirates on multiple occasions. Her role in the narrative is that of a formidable antagonist and a protector of Zephyr's will. She leads the attack on the Thousand Sunny, uses her powers against several crew members, and confronts Roronoa Zoro in combat. Her development is subtle, marked by the internal conflict between her absolute obedience to Zephyr and her own underlying doubts, which is perceptively noted by Zoro, who tells her that hesitation clouds her fighting. Her journey concludes with her grief at Zephyr's sacrifice, as she is ultimately forced to accept his final decision to face the Marines alone, leaving her future uncertain as she mourns his loss.

Her most notable ability comes from eating the Modo Modo no Mi, a Paramecia-class Devil Fruit also known as the Return-Return Fruit. This power allows her to generate a unique, harmless pink energy from her hands that can reverse the age of anything it touches by exactly twelve years with each application. She can fire this energy as projectiles or apply it through direct physical contact. This ability is extraordinarily versatile: it can weaken powerful opponents by reverting them to a less formidable younger state, and if applied multiple times to the same target, it can theoretically regress them to an age before birth, erasing them from existence. Furthermore, the power works on inanimate objects, allowing her to turn cooled volcanic rock back into deadly, searing lava or to solidify the ground to trap an opponent. The primary weakness of this fruit is that its effects are entirely undone if Ain is knocked unconscious or defeated, causing all aged targets to instantly return to their proper ages. Apart from her Devil Fruit, Ain is a highly capable combatant in her own right. She is an agile and acrobatic swordswoman who wields two daggers in close quarters and two pistols named Blackmaru and Akamaru for ranged attacks, demonstrating the physical prowess expected of a vice-admiral level fighter. Her strategic intellect is also notable, as she was able to secure her position as second-in-command by outmaneuvering a rival in a grueling five-hour battle.