Sirio appears as an 18-20-year-old boy with long, scruffy brown hair and yellow eyes. He has a longer midsection than normal, making him taller than normal. His outfit is the standard Synthetic Angel outfit, colored green and accented with brown. His wings are dark green with jagged feathers.
Sirio is a rare case, as his mindset was altered to that of a vicious dog. As such, he mainly walks on all fours (though he can stand), can only speak through barks and growls, and has an enhanced sense of smell. He is merciless in combat, drooling with malice as he savagely tears through enemies.
As mentioned above, Sirio has an enhanced sense of smell through his dog-like mind. His reflexes are excellent, and his speed is great (through outclassed by Senku). In battle, he is most proficient with Claws weapons, and wears two sets: One on his hands and one on his feet. The Sirio Claws are unlockable.
- Sirio is named after "Sirius", the brightest star in the night sky which is nicknamed the "Dog Star".