The "Her" role can easily be turned into a male role, FC: Brendon Urie!
They're opposites. Not just species-wise, but almost altogether they're just different. They immediately can't stand each other, total dislike, "Why can't I be bonded to anyone else" status. She likes dogs, he finds' a stray cat and takes it home. He hates being too warm, she turns the heat up. She likes to sleep, he uses his powers to invade her dreams and keep her awake- or at least feeling awake. He doesn't like Horns, she has her horns and tail out as often as possible, making it painfully obvious what she is.
Being bonded, they can't be far away from each other, so they're stuck around someone they absolutely can't stand constantly. He starts bothering her in her dreams just to annoy her back, because she's constantly doing her best to get on his nerves when she's awake. She's fully capable of kicking him out of her head, but she doesn't. He visits her every time she's asleep, even when he knows it's no longer annoying her. Eventually they start being nice to each other when they're both awake, too.
900-some years old. Powerful. Talented musician, artist. Intelligent, multilingual, extensive knowledge on most subjects. Stoic, serious, listener and watcher. Manipulative, but not as much as her. Charismatic, almost always in control of his emotions.
Her
200-some years old. Powerful. Talented technologically and all things gaming. Intelligent, multilingual. Stand-offish and rude, sneaky as hell. Manipulative, sociopath liar.