Sirius is the initial helper of Bomberman and later the main antagonist in the video game Bomberman 64, By collecting 100 Gold Cards and then defeating Altair, Sirius is getting an Omni Cube and become an evil.
Sirius was once the emperor of a planet who possessed a powerful item called the Omni Cube that gave him great power. But a band of mercenaries, consisting of Altair, Artemis, Orion, and Regulus stole the Omni Cube from him and used it to conquer planets.
Powerless without the Omni Cube, Sirius found someone who could help him restore his power: Bomberman, of Planet Bomber, which was experiencing its first invasion, by Altair. Sirius pretended he was a good guy and helped Bomberman fight against Altair several times, giving him remote bombs to fight Altair's monsters, Draco, Leviathan, Hades, Mantis, and Cerberus. He also made up stories about his life to Bomberman, saying that his home planet was destroyed by Altair, and that Altair killed his brother and sister.
At Stage 2 of Green Garden, Bomberman had to fight Sirius, who wanted to test him and see how powerful he had become.
After Bomberman defeated Altair, Regulus, Altair's only surviving associate, tried to save him, but both were knocked down by Sirius. Regulus fell over the edge. As Altair fell, he dropped the Omni Cube, and Sirius took it back and absorbed its power. He then kicked Altair into the air and vaporized him with an energy wave. He then revealed his true nature to Bomberman and threatened to destroy Planet Bomber.
Sirius flew to Rainbow Palace, where Bomberman eventually fought him. Sirius transformed the arena using the Omni Cube. He attacked by flying across the arena and shooting laser beams, which Bomberman can avoid by standing at the northmost or southmost part of the arena. After taking enough damage, Sirius attempted to kill Bomberman in the same way as Altair, but Regulus knocked him out of the way and destroyed the Omni Cube. Bomberman and Regulus teamed up and fought Sirius, and in the end they killed him.
He fell through space, sparking and flashing different colors while blue and orange beams of light came from him, and he exploded into shards of glass - easily the most elaborate and unique death scene in the game.
If a player beats Sirius and watches the true ending of the game, during the credits scene, outtakes are shown for the four minibosses as Bomberman fights them. For Sirius in Green Garden, he hits the edge of the arena as he is flying in and falls into the water.
- Bounce a pumped bomb off his head
- Catch him in a pumped bomb explosion
- Damage him (the pumped bomb explosion counts, and will get you both)
- Defeat him without throwing him over the edge
- Defeat him by target time
- Defeat his first form by target time (he may fall over the edge)
- Bounce a pumped bomb off his head (second form)
- Catch him in a pumped bomb explosion (second form)
- Regulus must be alive by the end of the fight
- Defeat him by target time
- "I guess I'd better help." (saving Bomberman from falling during the fight with Mantis)
- "Hahahaha!" (getting back the Omni Cube from Altair)
- "Hahahaha! Give it up!" (taking damage for the first time during the final battle)
- "Yo!" (before firing his anti-matter beam)
- "NOOOOOOOO!" (When defeated)
- "Now, let's see how strong you've become!" (while fighting him on Green Garden)
- "Better than I expected. Keep fighting like that and you should be able to defeat them. Good luck!"
- "It's been a while, Altair. Now that I've taken back the Omni Cube you stole from me, here's a present." (before killing Altair)
- "Bomberman, you've worked out better than I expected. Thanks for helping me regain my power. With my power back, I have nothing to fear. It was worth telling you all those corny lies, and helping you out. You've outlived your usefulness, you're starting to annoy me. Get ready to be destroyed along with Planet Bomber." (after killing Altair)
- Sirius is the second Bomberman villain to have similar traits to a Mario villain. In Sirius's case, he shares the role of one who helps the protagonist along the way, just to get the main villain out of the way so he can put his dastardly plans into motion, with Dimentio from Super Paper Mario. In this case, the role of Altair would be shared with that of Count Bleck, except that Bleck eventually turned good in the end, and Dimentio was never mistaken for a good guy, even when he revealed to the heroes that he was helping them fight Bleck.
- When Bomberman first goes to Green Garden, Sirius flies by and at the end of his talk he says "My name is Sirius - a name you should remember." His reason for saying this is likely because his name is never mentioned again in the game. When he is fought in Green Garden, the battle says "Friend or Foe" instead of "vs Sirius", and when he is fought in Rainbow Palace, the screen says "Final Battle".
- If a player fights Sirius in Green Garden after unlocking Rainbow Palace, it will now be a robotic version of Sirius. Similarly, if a player talks to him in the various levels, he will say "It is useless for you to oppose me. Lie down quietly and meet your end." The reasons for this are unknown, as Bomberman never canonically revisits the levels despite the player's ability to replay them.