BROTHERS, I HAVE CONNECTED THE DOTS.
Before you execute me for absolute heresy, hear me out. Sanguinius and Ahri from League of Legends are a perfect pair with the lore lining up so much it's terrifying. Let me explain before the Inquisition breaks down my door.
Both of them are profoundly lonely beings who view themselves as monsters. Sanguinius is terrified of his Red Thirst and losing his humanity while Ahri is haunted by her predatory nature and the memories of people she actually drained. They can literally sit down as they bond over the agony of fighting a feral hunger.
Despite their capability of violence both of them are very empathetic people. With Ahri being deeply valuing human connection and emotion while Sanguinius is one of the most kind and loving Primarchs in 40k.
Sanguinius is an artist as we know in 40k lore. He gave his sons the Blood Angel art as a way to not give into the Red Thirst. You know who else had a artist lover? Ahri, before she accidentally consumed her lover's soul.
Sanguinius is literally the ultimate artist boyfriend she wanted, except for probably being a 10 ft tall demi-god. Not only that, because of the Emperor stuffing two Baalite entities (Golden Angel and Black Angel) into the body of Sanguinius, his soul is a overflowing furance of warp energy. This means that Ahri can safely nibble off his excess psychic radiation. She gets his aggressive pressure to calm his Red Thirst, and in return she gets a infinite snack that doesn't have to die (unless Horus intervenes). They end up making a self regulating ecosystem that satiates both of their hungers.
You might even be asking, how would a fox girl even deal with a space vampire's bloodlust? Well you see Ahri's Vastayan Magic lets her manipulate emotions and project soothing illusions. When the Red Thirst awakens, she doesn't give him blood. She could weave an illusion of an Ionian forest into his brain, acting as a spiritual sedative.
In conclusion, the Blood Angels gets a step-mom who completely understands what it's like to accidentally eat people. Thank you for coming to my heresy talk.
TL;DR: They bond over accidental cannibalism, she gets an infinite psychic snack, he gets a magical sedative for the Red Thirst.