Random Thoughts: Hiei
I feel like contrary to popular belief Hiei would fall in love with a human. Someone who'd make him realize there is much more to strength to someone than just physical. Compassion and love are strengths as well. Sometimes rarer and more important. Someone whose determination can't be broken or stopped as easily, it's the sheer will that fascinates Hiei.
I feel like it would kinda be like how Sesshomaru and Rin met/came to be together. How it would take one kind-hearted human to help him when he's hurt just because they felt it was the right thing to do even knowing he could kill them with ease. Someone who refuses to be pushed or left behind. Someone who he could both be curious about without worrying about scaring them off. They could find the balance between human and demon and what works for them, with no rush.
This soft-hearted manner while he might feel slightly foolish, reminds him of his sister Yukina. Which of course, made him much more protective of you (and softer) on every and any occasion. ❤️🙂