Square released "Chrono Cross" for the Sony PlayStation in 1999. "Cross" is a sequel to "Chrono Trigger" featuring a new setting and cast of characters. Presenting a theme of parallel worlds, the story followed the protagonist Serge—a teenage boy thrust into an alternate reality in which he died years earlier. With the help of a thief named Kid, Serge endeavors to discover the truth behind his apparent death and obtain the Frozen Flame, a mythical artifact. Regarded by writer and director Masato Kato as an effort to "redo "Radical Dreamers" properly", "Chrono Cross" borrowed certain themes, scenarios, characters, and settings from "Dreamers". Yasunori Mitsuda also adapted certain songs from "Radical Dreamers" while scoring "Cross". "Radical Dreamers" was consequently removed from the series' main continuity, considered an alternate dimension. "Chrono Cross" shipped 1.5 million copies and was widely praised by critics.