We know that M's sensitivity and pheromones are a threat both to themselves and to others when not mitigated by the crystal they wear

We also know thx to b2 that whatever M went through was akin to torture in some sort of medical setting (they're wearing a medical gown in the mirror scene iirc, i'll need to replay b2 again to take a screenshot so i don't say bullshit here)

We ALSO know that human-vampires' special abilities have to do with their traits of when they were humans still

So, with M's relationship with their family being what it was when they were still human (i can't find the ask again but iirc it was hinted that it was tense in the "how would UB react if their parents didn't like the MC"), I'd theorize that the way they didn't build emotional relationships around them but only physical ones would hint at a willingness to use their physical senses to keep emotional responses at bay

BUT big vampire trauma happened and now they're physically overly sensitive to everything APART FROM THE MC

M's extreme hypersenses are a way for them to emotionally keep others at bay but also to keep them aware of their surroundings (the logic being "nothing can hurt/surprise me if i'm aware of everything around me"). That and like traumatic dreams, their brain is trying to prepare them in case the trauma happens again / find a way to heal from the trauma (the traumatic dream is a repetitive dream of the traumatic situation, which has the "purpose" of preparing the person in case the trauma happens again + the repetition of the dream is an attempt of the 'brain' to elaborate the trauma : example of Freud pointing out that war soldiers with physical wounds had less traumatic, repetitive dreams than soldiers with no physical wound -> the wound being a physical elaboration of the trauma allows for the trauma itself to be elaborated, the trauma and its affects find a representation in the physical wound -> properly linking affect and representation is basically the goal in therapy, we unlink things to properly link them back ☝🏼🤓)

That and the pheromones allowing them to influence/control someone's emotional state which is a wonderful thing to have to a) make someone like you, b) make someone agree with you / make things go your way, and ofc c) make someone not do what you do not want them to do

Thing is, M's extreme hypersenses calm down when they're with the MC BECAUSE there is no need to keep them at bay, they're emotionally safe and won't hurt them the way they've been hurt in the past (yes UB is safe too but not on a soulmate kind of way and idk how else to justify it just let me have this plz 😔)

Conclusion is that while M's special abilities find their root in M's life as a human, their extremeness could be explained by the repetition of their human trauma in their vampire life