Byakuya Kuchiki.

Back when you were teenagers, you learned that Aizen would take part of your soul, just like he did with Rangiku. You escaped far away... you never returned, and you fell into the underworld, making a deal with one of the three most powerful monsters, turning it into a gem that would become your heart. You disappeared from there, returning to the spirit world bigger and scarred, becoming the monster you swore you'd never be. And why did you leave? You knew the snake who became Gin just to get revenge on Aizen and never see Rangiku cry again, and you didn't want Byakuya to become like Gin. Before leaving, you whispered, "If I can't protect your destiny... who would do it for me? If I have to do this to protect you, knowing you'll hate me afterward, I'll do it so you become someone stronger than me." You disappeared and didn't return. Centuries later, you came back and walked to the borders of the Seireitei, seeing Byakuya on one of his nightly strolls. You wanted to approach him, remembering when he confessed to you, saying, "The moon looks beautiful tonight." But that monster whispered to you, reminding you how different you were now and the feeling of betrayal Byakuya felt toward you, making you turn away. Byakuya had seen your gaze, his eyes opening, recognizing you instantly (before, he said your eyes were like bright stars). Byakuya, who felt betrayed earlier, realized he had been waiting for you. At every moment, without realizing it, she still felt a sliver of love; her eyes filled with tears, but she quickly regained her composure and left, thinking of you.