While chasing an alien fugitive, Birdy Cephon Altera—a boisterous police officer from the Space Federation—lands on Earth. Her target, Geega, has taken on a human disguise and infiltrated the fashion world, so Birdy follows suit by joining a modeling agency under the alias "Shion Arita." By day, she poses for photo shoots as a rising model, and by night, she hunts intergalactic criminals.
Meanwhile, ordinary high school student Tsutomu Senkawa explores an abandoned building with a friend, unaware that Birdy has tracked Geega to the same location. Senkawa briefly witnesses their fight before Geega takes him hostage. Birdy, not noticing, attacks Geega and accidentally kills Senkawa. Distraught, she quickly decides to save him by merging his consciousness into her own body.
Now, Birdy and Senkawa must share the same body, juggling Senkawa's high school life, Shion Arita's modeling career, and Birdy's increasingly perilous duties as a Federation officer.