In the aftermath of the Ryunka disaster, Tokyo grapples with social unrest. The aliens responsible for the catastrophe are on the run on Earth after fleeing the Space Federation. Birdy Cephon Altera, a Space Federation officer sharing a body with high schooler Tsutomu Senkawa, is assigned to apprehend the fugitives. But complications arise as they become the hunted, targeted by a mysterious assassin seeking vengeance. Juggling daily turmoil and a hunt for the assassin's true identity, Birdy races to prevent more escapees from meeting a grim fate.