The Enchantress
As a daughter, Heimdall does what her mother says. However, she doesn't seem to fully agree with her mother on the subject of demons, even though she mostly does what the Enchantress expects from her.

Meteora
Heimdall enjoys the company of her pegasus cousin Meteora, with whom she can take a break from her Vicereine role. He often checks on her and tries to cheer her up, knowing the difficulties of his beloved cousin.

Mémoire
Heimdall is haunted by the presence of Mémoire, who appears as the manifestation of her fears and insecurities, similarly to Kiersten's mind monster. This entity often manifests during her moments of doubt, exacerbating her internal struggles. Even if the noctule is not alive anymore, he lives on in Heimdall's mind and memory.

Heimdall was born in the clan, from the union of a pegasus mare, the Enchantress, and a unicorn stallion, the Viceroy Vif-Argent. Since birth, her life was planned, as she was destined to become the next Vicereine of the clan. Due to unicorns' disappearance, she lost her father at a very young age and was raised by her mother, who raised her to do exactly what she wanted. It is currently unknown how Heimdall survived the extinction.
Since her first appearance in the story, Heimdall questions her mother's radical choices, especially regarding demons. She still decided to spare the noctule litter that her cousin Meteora found, even if it meant disobeying her mother.

It is later revealed that Heimdall is quite scared of adult noctules, as she had a traumatic experience with one when she was younger - this particular noctule tried to lure her out of the Nest by using her deceased father's voice. This has led Heimdall to be very wary of noctules - even if she still decided to spare the fawns.
After the discovery of a pegasus' body killed by Kiersten, Heimdall is forced by her mother to speak to the whole clan, and has to follow the majority's opinion on demons. She reluctantly agrees to make the demons pay for this, but it seems that this is not what she truly wants. A conversation with her cousin, Meteora, shows that she is quite lost about what she has to think about.

Later on, Heimdall confronts the Enchantress one more time on the subject of demons, only to be told the same thing over again. After wandering a bit in the Nest alone, she experiences a traumatic vision of the noctule who attacked her as a child - he is still haunting her, even in death, manifesting her fear of the future and the weight of her responsibilities.