Happy Girl
Disclaimer: I don't own Yu-Gi-Oh!
He never really liked her. No scratch that, he hated how she was always such a happy girl. Always telling her friendship speeches, and how she was a cheerleader for them. She was always such a happy girl, while he was too busy to have any such emotions that she conveyed to him. And then one day, she told him something, about how he really truly was. He had no one to tell him what to do, or how to act. The only person he ever truly had was his younger brother, Mokuba. But at that moment, he saw that she could truly understand him, his lonely soul. He thought that happy people can never see nor understand people like him. And yet she did. He could understand why she was always with them, rotting for them.
And then came his own tournament, trying to beat Pegasus in the sense, that his tournament was better than Duelist Kingdom. However, he got trapped by his own adopted father's son, which he never knew his adopted father had children. And then he saw her pity, when everyone heard about his own life story. Now, everyone could understand why Seto Kaiba was so cold, and that if he and Mokuba were never adopted, maybe then he would never be such a cold person. But he then remembered what Tea told him, at Duelist Kingdom, how he had no heart, or friends. For that moment he felt alive, he felt the reason why life was worth living for. Not just for Mokuba. He should have thanked Tea then for giving him a moment of feeling his heart again. The same heart that he shut out of his life.
He was glad that his adopted father tried to take Mokuba away from him, because at that moment he realized that another person was put in his heart. (And also that he knew how to fight for his brother's life, while for someone else he wasn't sure). He was glad his adopted father didn't try to see all the way into his heart. He'll protect his heart, and make sure that no one else knows how he felt about her.
He understood why Tea came to all the adventures with him and those pipsqueaks. He was glad he had another reason why to live. And he was glad that in the end, everything turned out all right.