Roberto serves as one of three main characters in the science club with Ryuta Hoshikawa and Patrick. He stands as the only brown Latino member, enhancing the group's cultural diversity. Their visit to a Thomas Edison museum exhibit, specifically learning about his proposed "spirit phone," sparks the plot and initiates their spiritual adventure.

Roberto exhibits a passionate, often impulsive nature, contrasting Patrick's initial skepticism. His emotional reactions, including frequent arguments with Patrick, directly shape their experiences in the Spirit World. For example, their bickering in the Posthumous Realm creates a hole that swallows them, illustrating how negative emotions manifest consequences in spiritual dimensions. Later, entitled behavior and complaints about unfair exclusion at the gates of the Bodhisattva Realm cause them to fall into Hell, reinforcing the thematic link between mindset and spiritual fate.

After falling into Hell, Roberto and Patrick become distressed captives, trapped in the vines of a demonic tree. This positions them as victims requiring rescue by Ryuta, Yuko, and their guide God Eagle. Their captivity underscores the film's exploration of deliverance from damnation, as their companions later free them.

Roberto's skepticism toward the Spirit World diminishes after his rescue, transitioning into belief as he witnesses spiritual phenomena firsthand. This development aligns with his role as a foil to Ryuta's spiritual openness, ultimately leading him to accept the existence and mechanics of the afterlife presented during their journey. Roberto appears exclusively in the 2006 film.