- First Son: "Tell me why, Jedi. I stand unique among all other men in the galaxy. Why must I be destroyed?"
- Barsen'thor: "There is more to you than the First Son of the Emperor. That part, I must save."
- ―The First Son and the Barsen'thor.[src]
During the Second Great Galactic War between the Galactic Republic and the Sith Empire, Republic and Imperial forces clashed on Corellia during the Battle of Corellia. While a Jedi Knight known as the Hero of Tython led the Jedi and Republic forces against the Empire, the Barsen'thor entered a cave system and faced off against the First Son of the Children of the Sith Emperor, Jedi Master Syo Bakarn.
The First Son was the most powerful member of the Children of the Sith Emperor, shielding the rest from detection. The Barsen'thor, having defeated numerous Children already, knew the rest could not be defeated unless the First Son was. The Barsen'thor learned of the First Son's identity, his whereabouts, and set out to face him.
The Barsen'thor found the First Son in the caves of Corellia, the First Son's homeworld. The First Son quickly masked his connection to the Force, and while cloaked, hit the Barsen'thor with a powerful Force-Push, and followed with a blast of Force lightning. At that moment however, the Barsen'thor reached out with the Force, and sensed his opponent. The Barsen'thor used a powerful Force-Push to stun the First Son and give enough time to scramble to safety.
Having already faced many Children already, and now familiar with the First Son's cloaking technique, the Barsen'thor engaged in a brutal duel with the First Son. The First Son attempted to use numerous Force Powers, many of which were swatted aside by the the Barsen'thor. Each time the First Son tried to mask his presence, he was detected by the Barsen'thor. His Force Powers and Lightsaber strikes were deflected; the duel was in the Barsen'thor's favor.
After a furious exchange of Lightsaber strikes and Force Powers, the Barsen'thor prevailed, wounding and defeating the First Son. The First Son made a final attempt to prevent destruction by asking why he must be destroyed. The Barsen'thor replied that it would save lives; by redeeming Syo Bakarn (one of the greatest Jedi healers and most devoted Republican combatants), the Republic would become stronger, while the destruction of the First Son would take away the most powerful Child of the Sith Emperor and unmask the other Children, thus debilitating the Empire. This destroyed the First Son by redeeming him as Syo Bakarn.
The Barsen'thor successfully redeemed the First Son as Syo Bakarn again, but the latter decided to stay on Corellia to heal from his dark ordeal. The Barsen'thor returned to Coruscant, where the Barsen'thor was celebrated as a hero and received Syo Bakarn's empty seat on the Jedi High Council.
- Star Wars: The Old Republic (First appearance)