Hana no Hana - Inariya Fusanosuke - One of my Fave yaoi manga In no order.

He could hear her still at times. ‘Promise me’, she had cried, in a room that smelled of blood and roses. ‘Promise me, Ned.’ The fever had taken her strength and her voice had been faint as a whisper, but when he gave her his word, the fear had gone out of his sisters eye’s. Ned remembered the way she had smiled then, how tightly her fingers had clutched his as she gave up her hold on life, the rose petals spilling from her palm, dead and black.

They had come together at the ford of the Trident while the battle crashed around them, Robert with warhammer and his great antlered helm, the Targaryen prince armored all in black. On his breast plate was the three-headed dragon of his House, wrought all in rubies that flashed like fire in the sunlight. The waters of the Trident ran red around the hooves at their destriers as they circled and clashed, again and again, until at last a crushing blow from Robert’s hammer stove in the dragon and the chest beneath it. When Ned had finally come on the scene, Rhaegar lay dead in the stream, while men of both armies scrabbled in the swirling waters for rubies knocked free of his armor.

- George R.R. Martin - A Game of Thrones. Lyanna Stark and Rhaegar Targaryen.

To save those she held dear to her she gave her enemy her true name. She would become the sacrifice that would resurrect the great Demon King Arawn. Deep under a spell she was taken before him.

"I am your servant" she said to the Demon King

"I am your servant, Your holiness. I am the servant of you, the one and only invincible god. I will obey and love only you for all eternity."

He looked deep with in her soul and spoke with her away from the ears of others. He asked her to open her eyes but she didn’t. again he asked.

I want you to open your eyes.”

She heard his voice through the darkness, it sounded new to her but distance  "A voice of a stranger" she mumbled “Excuse me, who are you?”

"I am Arawn.” he replied.

"Lord Arawn, where are you?" she asked.

"I’m right in front of you."

"I apologize, I have lost my ability to see. From the moment I revealed my true name, there has been nothing but darkness before me."

As they continued speak he showed her though his eyes what he could see. She saw her brother coming to save her and the man that had brought her forward as a sacrifice baring his path. She smiled, Her brother had come to save her, it made her feel happy briefly before Arawn pointed out as long as she was under this mans control they would both meet their death. She knew what she had to do so she asked the Demon King for one thing.

"Please tell him that I am sorry. I, Riannon, have already lost the power of the true name. I can no longer protect the honor and covenant of our tribe. I am not worthy of my brother and the others coming to rescue me, so please tell him to leave quickly."

"Honestly why? Why are you saying such things?" 

The Demon became sad and angered by this. This girl was ready to give up everything, such a brave and sweet girl, ready to become a sacrifice. It gave him the incentive he needed. He was going to save her. He was going to set her free. 

- Tears To Tiara. Otp First meeting. Mixture of the animes quotes and my writing.

And he never forgave.

And he never forgot.