Alice hates humans as well, but I'm not sure if it's to the same degree (i.e. "round them up into human ranches and systematically kill them hundreds at a time"). Though, they can relate to the "My family is dead because I should have been able to protect them" conundrum (Martel for Mithos, Alice's parents for Alice), thinking power is the only way to make things change, and of course, both being half-elves.

Mithos liked Alice because of how much they had in common. Same was the case with Alice, though she also liked him because of her fetishization of power, and it doesn't get much more powerful than Four Seraphim. That was also one of her goals: "I want a Cruxis Crystal."

That's not to say the relationship was perfect. She was still borderline abusive (though not as much as she could be), and he was basically fixating on her as a replacement for Martel while dealing with his 'everyone ever betrayed me' deal and constant victim complex, which isn't healthy.