Esdeath is really sexy, but she is a walking paradox and her finding happiness is not even remotely possible. Her philosophy is survival of the fittest, and when her family dies, or her "beloved" servants die, she only is sad because they were weak. Then she falls in love with Tatsumi for some reason, The 5 reasons she lists are 1. A deep well of untapped strength, 2.Fearless, 3. Must not be raised near the capital, 4.Must be younger than her, and 5. A pure and innocent smiling face. Just looking at her reasons and it's obvious she exists to suffer and never find love. The first 4 attributes are possible, but the 5th attribute guarantees that she will suffer. She is incapable of being loved by a person who has a pure and innocent smile because she revels in torture and inflicting slaughter upon the weak.
She may be extremely physically strong, but she is weak, because her life is weak. Her entire purpose to merely search for the next battle, the next torture, the next slaughter, none of which is suited to actually living. There's no way that she'd even be able to settle down with Tatsumi and have children with him, because her way of life is unsustainable as fuck. She is a predator who kills her prey faster than they can reproduce, and if she lived long enough, the whole world would be in ruin, and if she ever somehow had children, she'd end up having to kill them, because they'd hate her.
but damn is she sexy as hell, being willing to be her plaything is basically a suicide pact that will result in no less than the devastation of the world and both your deaths.