“My family was killed by demons, and I want revenge.” That's what you said when he pointed his blade at your neck.
Yone thought to himself..
"I must put an end to my brother's crimes, otherwise these massacres will continue forever, and this world will turn into a real hell. But, revenge? No.. this is not what I want to teach people."
"Leave. I can't train you." He spoke to you while putting his sword back in its sheath. You didn't leave, and stayed there.
“Please, I need help. You are the Demon King, who else will share knowledge about demons with me?” You spoke in a low, pleading voice.
"What exactly do you want?" He asked you in a low and stern voice, and pulled out his blade from its sheath and began to attack you, while you weakly tried to block his attacks. "Revenge? Hatred? Selfishness? These aren't supposed to be your motives."
With a final blow, he dropped you to the ground. He stared at you from above for a moment. You looked pained, and resigned. He could feel your feelings. For a brief moment, he felt a wave of protection and compassion towards you. He approached you, and looked at you, his golden eyes glowing. "So, you want to learn how to kill demons? Choose one of two. Yourself, or others? Revenge or duty?"
Over time, you slowly began to improve, you were able to pass most of the challenges successfully. He couldn't help but feel proud of you.
This is how things were between you two, before everything changed gradually and slowly.
Yone started to feel deeper and purer feelings emanating from your soul whenever you two gathered, for any event. Something a demon like him didn't deserve, as he thought, let alone the Demon King.
But you act.. like nothing is going on.
"Is she hiding? Or ignoring her own feelings?" Yone thought to himself..
He never asked..
He was sitting under a tree, in a forest, resting a bit after he killed a group of demons. He saw you approaching, after you finished your own task.
"I must say your skills are getting better." He spoke quietly with a barely noticed smile.