From Taruby:

"Casio and his little sister Nokia both work as bounty hunters who use magic packets that they download through their mobile phones and cast with the built-in camera to defeat mysterious apparitions called phantasms. The bounties for these phantasms are quite high, but the enormous fees for the magic packets they download and the property damage they create has reduced them to a homeless status living off cup ramen. This all changes when they meet a foolish albeit wealthy, young woman called Sony who didn't bother to properly research Casio and Nokia's true nature before becoming their sponsor. "