While pursuing alien criminals named Bacillus and Geega, Birdy and Tute infiltrate Earth under the cover of a rising Japanese idol and her manager. During one night on a routine mission to apprehend the said criminal, a civilian named Tsutomu Senkawa is used as a human shield. When Birdy realized that she killed him in an accident, she decided that the only way to save his life was to fuse her body with his in order to prevent him from dying. Tsutomu thought that it was all a dream until he found that he was unable to control his body one night after he was supposedly dead.

Birdy and Tsutomu try to cope with existing by sharing one body, but leading two separate lives. Birdy's commanding officer, Magius, informs Tsutomu that his original body's being restored and it will be some time before he can live outside of Birdy's body. Bacillus tries to eliminate Birdy by luring her into a movie shooting as cover. Keisuke Muroto tries to take photos of Bacillus and Birdy, but falls unconscious when he was knocked out by debris. A wounded Bacillus took over Geegar's Earth body as his first one was damaged from deterioration and from fighting Birdy.

Bacillus tries to locate and eliminate Birdy, while she, Tsutomu and Tute argue over the constant separate lives that they were trying to hide from the public. Tute gets wounded by Bacillus before he gave Birdy an Elemental Destructor capsule bomb to kill Bacillus and eliminate the threat of him killing an Earth-born civilian in Japan. Birdy mourns Tute's death when he can't heal his wounds from Bacillus' attack.

Continuing the memory dive, Tsutomu learns more of the Central Tower attack and Birdy's part within it.

The School Festival opens where Hayamiya gives her piece on the disaster refugees. Nataru finds and severely wounds Gatoru before he and Moss escapes. Hoping to cut a deal with Revi Moss kills him but is rejected and decides to fight Nataru win or lose.

Nataru and Moss fight but Moss is nearly killed before being rescued by Birdy who attempts to convince Nataru to surrender and receive treatment before his Iksiola state kills him. He refuses and nearly kills Birdy before Senkawa switches in and convinces Nataru that being an Iksiola means more than just killing. Nataru relents and jumps back in time to the moment of the tower attack becoming the man who saves a young Birdy via a time-loop.