Aru-Wen was a Jedi Master during the time the Jedi Order was at war with Sith Lord Kaan's Army of Darkness. As a Padawan, Aru-Wen chose the young Set Harth, but was often concerned that Set Harth preferred to use violence to solve problems. This deeply troubled Aru-Wen and it was for this reason that he did not take Set along with him as he joined Jedi Master Hoth's Army of Light to battle against the Sith forces.
However, Aru-Wen, along with many other Jedi Knights and Masters was killed on Ruusan when Kaan set off the thought-bomb, decimating the Jedi as well as Sith forces, and thus ending the war. His master having become one with the Force, Set Harth was left without an instructor. Rather than seek a new teacher from the surviving Jedi, Set Harth preferred the road of independent study, and unfortunately, without a master to guide him, Set Harth only continued his violent ways and was eventually seduced by the Dark Side, becoming a Dark Jedi. The Dark Side claimed not just Aru-Wen's life, but Seth's as well.