Capella Titis hails from the same planet as Birdy Cephon Altera and serves as an observer on Earth. Cautious and solitary, she operates with a dedicated guardian acting as both protector and scout. Her core mission focuses on monitoring the organic superweapon Ryunka and its connection to media magnate Satyajit Shyamalan, whose nihilistic goals align with her interests. To facilitate Ryunka's development, Capella implants it within human student Sayaka Nakasugi, actively interfering with Federation operations to advance this objective.

Stranded on Earth after catastrophic events in Tokyo, Capella seeks refuge with Irma, a figure in the series' underworld. Irma grants sanctuary but assigns Capella menial housemaid duties while covertly manipulating her circumstances. This situation parallels Birdy's own experience but fuels Capella's growing antipathy towards Birdy's civilian identity, Shion Arita.