It was a metallic taste in his mouth, the scent of her fear.
A greater aphrodisiac could not to be found. It lifted the distaste that he held towards human women, awakening that last part of the beast he kept locked inside. It also comforted him because she was not afraid of him. She was afraid of her own desires.
He saw the tainted arousal in her eyes when she was in pain. In the few times he saw her bound, he knew her desire to be even more enchained. He knew her dreams. He knew her fantasies, because they were the same as his.
His brother, naïve to pleasure, ignorant to anything except a dead priestess and the aspiration to increase the strength of his Tessaiga, did not know or recognize what that extra tang to her scent really was.
And now she knew that he knew. All he had to do was catch her partially glazed eyes as Inuyasha cut the ropes on yet another occasion.
He had thought, before, that she was just weak. Now, it was obvious to him the reality.
Still unfettered by an attachment to the group, he could shadow their movements. Leaving his own a safe distance from the others, and suppressing his power, he waited patiently at the nearby hot spring. When she was left to finish by herself, he appeared behind her, silent, deadly.
Twisting her arms and yanking her towards him, he whispered into her ear, "I know what you've been hiding," relishing the sound stifled in her throat. Her shudder was all the answer he needed, the skin of her neck pressed against the spikes of his armor.
"I will relieve you of your guilt," his tongue traced the line of her ear as he spoke.
He knew the answer in her awakening arousal and the trembling of her body before she gasped with yearning.
"Please."