Sirius is a low-ranked gun that provides 18 Attack, 10 Evade, 51 CT, and 5% Combo Rate. It requires the Guns 3 license to equip, and can be bought for 4,000 gil at Rabanastre and Jahara, stolen from Wooly Gator (3% chance), or found in Dalmasca Estersand (The Yoma) or Golmore Jungle (The Rustling Chapel).
In the International version, it now provides 17 Attack, 10 Evade, 50 CT, and 5% Combo Rate. It can now be bought for 2,600 gil at Rabanastre, Nam-Yensa Sandsea, Tomb of Raithwall, Jahara, and Balfonheim Port, stolen from Wooly Gator (3% chance), or found at Ogir-Yensa Sandsea (Primary Tank Complex) or Nam-Yensa Sandsea (Simoon Bluff).
Sirius appears not as a firearm but rather a star globe for Astrologians, one of the Gerolt Masterworks weapons. It requires level 50 or higher to equip with an item level of 110, and provides Vitality +44, Mind +42, Piety +23, Accuracy +9, and Spell Speed +44.
Sirius is the brightest star in the night sky. Sirius is also known colloquially as the "Dog Star", reflecting its prominence in its constellation, Canis Major.