Volcanica/Relationships

Satella
Volcanica seems to hold itself responsible for the events that had transpired 400 years ago, though it's not specifically stated why the dragon blames itself. It is also shown to have been rather close to the girl as when reminded of her, its eyes were full of sorrow and regret. Volcanica also said "they" cannot rise their heads in front of Satella and if Satella got hurt, it was Volcanica who would be blamed, serving only as further proof of their close friendship before the catastrophe struck.

Farsale Lugunica
Farsale was the first of all humans who was strong enough to not cower before the Divine Dragon. He also asked Volcanica to help him protect the Kingdom of Lugunica in times of need. They seemed to have been sharing a rather close and friendly relationship as Volcanica was speaking rather fondly of him, during the dragon's faceoff with Emilia in Arc 6's climax.

Flugel
The relationship between Flugel and Volcanica is mostly unknown but it's safe to assume the Sage and the Divine Dragon were on friendly terms as they collaborated in the battle against the Witch of Envy, 400 years ago. Volcanica also mentioned it's bound to the tower with a contract; a contract most likely made between him and Flugel himself.

Echidna
While it's not known what kind of relationship the Divine Dragon and the last Witch of Greed had, however, Volcanica was the one that kept Echidna's soul in her grave for four centuries as a deterrent to Satella.

Roswaal L Mathers
Roswaal's grand plan is to defeat and kill the Divine Dragon, for reasons yet unknown. According to the author, Echidna has nothing to do with Roswaal's goals as, even if he'd learn of Omega's existence, he would've still wanted to kill the Dragon.

Emilia
Emilia and Volcanica faced each other during the climax of Arc 6, as Emilia was tasked with passing the 3rd Trial of the Pleiades Watchtower, which was being overseen by the Divine Dragon itself. Upon first laying eyes on the Divine Dragon, Emilia felt like she couldn't even breathe in the dragon's presence without its permission. Though she tried to start a conversation with the dragon, due to its hibernation-like state, no such thing was possible. Instead, due to the nature of the trial, the two had to fight each other. Despite the dragon being in the aforementioned state and displaying roughly 10% of its original power, it nearly killed Emilia on at least two separate occasions. Some time during their fight, however, Volcanica regained its "self" and gave Emilia the chance to converse with it. However, the debate didn't last long as Volcanica mistook Emilia for Satella, started apologising and attacked the half-elf girl with an intent to kill.

Patrasche
Upon meeting her, Volcanica was somehow able to recognize who Patrasche was, calling the Land Dragon's name in surprise.