(for the ask game) 1, 6, and 16 for vasiddon :3
1- What do you think is the appeal of their dynamic?
Their appeal to me from the moment of conception has been two people of very different backgrounds and approaches to life brought together and made to interact with one another.
Their relationship shouldn't work, and yet it does. They start as imbalanced as can be, with Abaddon holding complete power over her, and end up with Vasi getting a tight grip on his leash.
Now, I don't think Abaddon is the kind of guy to let someone pull him around for long, he does not simply submit (and if he does it doesn't last) but he sees merit in letting go. She anchors him in a way very few can, and he in turn takes care of her. Kind of.
For Vasi it's a little more complicated. She does not initially reciprocate anything romantic from his side, still grieving over Horus, but finds herself unable to wish harm on him. Abaddon and the Vengeful Spirit are the sole remains of her past life, and she cannot let them go. She will sacrifice herself time and time again to make sure of it.
6- In what ways do they complement and complete each other?
Because their fields of expertise differ so much, there are many aspects of one that the other fulfills. Abaddon as a warrior and army leader and Vasi as an artist and entertainer. When working together in harmony they fill different needs aboard the Vengeful Spirit, as well as eachother's.
They complement eachother by taking up the place of a destroyer and a creator respectively. Abaddon has no desire to rebuild after he has left the galaxy burning, but Vasi does. Whereas the Warmaster carries himself as the domineering and uncaring tyrant with a charm sharp as a blade, his songbird is soft and considerate, and she shows patience in places her master would not tolerate.
It is no accident that Vasi has been dubbed "Abaddon's Mercy" by some.
16- How accepted is their relationship by their community and loved ones?
For Vasi it's hardly something anyone who had known her previously would ever want for her. But they are all long dead now, so it's not like it really matters.
As for Abaddon, he is the gods damned Warmaster, and no one will ever get a say, whether they approve or not, of such personal matters to him. That being said, the few brothers who are close to him still, such as Falkus Kibre, would probably not really care so long as he keeps the Legion in power.