The story behind "Otherworld," the song that changed the sound of "Final Fantasy."

Tidus and Yuna remain two of the most iconic protagonists in the "Final Fantasy" series.

Around the turn of the millennium, straight edge hardcore singer Bill Muir was asked by Japanese game developer Square (now known as Square Enix) to lend his vocals to a song for its upcoming RPG, Final Fantasy X. It seemed like just another recording session. Instead, it became the opening track to one of the most beloved games in the series. Twenty-five years later, "Otherworld" remains one of the most iconic video game openings ever made.At first, Final Fantasy X lulls players into a familiar rhythm. Gentle music plays over the opening menus, evoking the orchestral soundscapes longtime fans had come to expect from the series. Then, just minutes into the game, Muir's ferocious vocals rip through the silence. As Tidus awakens and flashes back to his former life as a blitzball star in Zanarkand, "Otherworld" explodes onto the soundtrack, replacing tranquility with pounding guitars and raw aggression. It's a startling introduction that immediately announces Final Fantasy X isn't interested in playing by the series' established rules.