Uncanny X-Men (1963) #480

The Rise and Fall of the Shi'Ar Empire, ch. 6
"Vulcan's Progress Credux"

Vulcan engages the Imperial Guard in battle, and finds that he's not as ready for them as he thought. He kills Impulse and severely wounds both Cosmo and Neutron, before Nightside envelops him within her dark void. Her attempt also fails, and Vulcan manages to take her out, along with Oracle and Hobgoblin. Only Gladiator appears able to handle Vulcan, and he lands some punishing shots, taking Vulcan's left eye out as they fight. Ultimately, Vulcan is left unconscious. The Vice-Chancellor orders Gladiator to have Vulcan brought to a prison orbiting Phygim and, there, Vulcan is shackled, unable to access his power. He is also given a synthetic eye. He can't determine how long he is there, and at one point he dreams of his younger self. The child taunts the older Vulcan, who calls him a widdle baby; a fifteen-year-old with the maturity of a thirteen-year-old. Eventually, Vulcan is woken by a soldier working for the vice-chancellor, a member of the Secret Order, who would like Vulcan to work for them. He asks Vulcan to go down two levels and see what awaits him. Vulcan does so, killing a few guards on the way. Two levels down, he discovers Deathbird, who he inadvertently releases from her cell.