Phantasy Star Universe: Ambition of the Illuminus (Japanese: ) is an expansion pack to Phantasy Star Universe. It continues the story from where Phantasy Star Universe left off. Players use their own avatars and take the role as instructors to younger GUARDIANS recruits while investigating the evil organization of "human supremacists" known as the Illuminus. Along with new missions, new weapons are introduced as well as new Photon Arts, classes, enemies, bosses, and more. The user's personal avatar is the main character. In Phantasy Star Universe, players experienced the story through the eyes of Ethan Waber. In Ambition of the Illuminus, they will complete missions using their own customized avatar, working to restore peace in the Gurhal System. This content is available offline in the PS2 and PC versions; there is no expansion offline content available on the Xbox 360, however.
On November 13, 2008, this expansion was available on the Xbox Live Marketplace for free (reduced from its original price of 1600, then 800). PS2 and PC players have to purchase a retail disc of the expansion for $19.99. These were both released on November 20, 2007.
As of June 30, 2010, the expansion became free to download on Xbox Live Marketplace. A new version which is currently required for online play was released on July 20, 2010 and contains GUARDIANS Advanced Content.