Lenny Ai, sometimes called Jenny or Lennie, is a 16-year-old Martian who turns 17. She lives under Commander Hazzard Pascha's oppressive rule and fears for her family's safety on Mars, facing Hazzard's persecution. Fleeing Martian military police with friends Joe Maya and Mike Coil, she discovers the crashed alien ship Xenos 5 under attack, beginning her involvement with the Ladorian aliens and their ninja robots.

She pilots the ninja robot Phoenix Thunderhawk (also known as Houraioh or Crimson Falcon), becoming the second after Joe to operate such a machine. Her combat style is daring and skilled, nearly matching Joe's boldness, and she rescues him multiple times. Though often tomboyish, she shows a caring, sensitive side, especially concerning her family and her feelings for Joe.

Her character arc centers on her passionate, largely unreciprocated love for Joe Maya. She reacts with jealousy and possessiveness, visibly hurt or angered by his insensitivity and occasional flirtations with Princess Romina (or Rowena). This tension escalates when Romina admits her own love for Joe. Lenny and Romina eventually form a truce, agreeing to unite against the Zaboom army to liberate Ladorio, despite Lenny's fear that Joe might choose Romina.

A local boy, Kenji, has an unreturned crush on her, and Joe's teasing about it irritates her. Her relationship with Mike is close and sisterly; she supports him emotionally and advises him on his romantic interest in Jade, the princess's attendant.

Her motivations shift significantly: initially driven to protect her family and rebel against Hazzard, her goals expand to aiding Ladorio's liberation after Joe confesses his love, easing her fear of losing him to Romina and solidifying her commitment. Her decision to accompany the group to Ladorio, despite earlier reluctance, marks a key point in her development.