Regulus Corneas/Relationships

Pandora
Pandora persuaded Regulus to accompany her to attack Elior Forest and succeeded. Also, Regulus sees Pandora as a higher ranked member of the Witch Cult, unusually referring her with "sama"

Petelgeuse Romanee-Conti
Regulus seemed to be acquinted with Petelgeuse and was a fellow member of the Witch Cult. Petelgeuse entrusted Regulus on not bringing Pandora to Elior Forest but he betrayed him and the Elves village.

Natsuki Subaru
Subaru confronted him during Regulus' and Emilia's wedding in Priestella. Following into a battle with Reinhard van Astrea joining the battle and concluding into the death of Regulus.