Jannis, a solitary space pirate, accepted a contract from fellow pirate Shiunk to track and capture the Agga Ruter spaceship. She foresaw Shiunk's betrayal and deployed a decoy, resulting in Shiunk's defeat when the authentic Agga Ruter overpowered his vessel. After this confrontation, she renounced piracy and allied with Taiyo and Kei on their mission.

Her past holds a traumatic adolescent incident: a circus owner took her in and became her boyfriend, but she underwent a beastly transformation during sexual arousal and accidentally killed him. Terrified of her lethal nature, she withdrew into obscurity and embraced isolation as a space pirate to prevent harming potential loved ones. She crewed her ship, Lyla, solely with small robotic assistants to eliminate risks to organic beings.

Biologically, Jannis descends from genetically modified humans who altered their DNA for harsh-environment survival. While her race largely reverted to human form, her pheromones trigger a reversion to a bestial state during arousal. This transformation halts only upon achieving orgasm, requiring a partner both resilient enough to endure her attacks and skilled enough to satisfy her. Taiyo proved capable of this, cementing her choice to stay with his crew.

Later, her ship Lyla was destroyed during events aboard the Millenia Amour. Space pirate hunter Yvonne captured and imprisoned her afterward. Taiyo secured her freedom by forming a romantic relationship with and marrying the prison warden.

A minor trivia note mentions her wearing Cabbit ears once.