Yili has no desire in her heart. He has been pursuing happiness since he was sensible. Because he is different from ordinary people, he can't feel what happiness is. The so-called desire is what is produced by dissatisfaction with the status quo. He didn't have this thing in mind, but his father gave him this name, which has a clear and beautiful meaning. He didn't feel that way once for all the beautiful things his father said. He doesn't understand. So he spent all his life on it before the Holy Grail War, but no matter how hard he tried, he couldn't get such a common feeling that he was born with a defect. If he didn't have it in the first place, then what did he come to this world for? After many failed attempts, he began to stop pursuing, but questioned why he did this. After taking part in the Holy Grail War, he got the answer through glittering induction. He just doesn't have the happiness that ordinary people have. He can't feel any beauty in what others think is beautiful and believe, but he will find happiness in the opposite of human nature. But just because he has common sense, he thinks he can't indulge himself to pursue such happiness, and Yili's inner doubts can't be solved for a long time, which makes him angry. But the essence of "all evil in this world" in the Holy Grail makes him think that "all evil in this world" can give him the answer he wants to know, but he can't get the answer himself, so he hopes that something that can get the answer can be born, even at the cost of death, because there is no other way. If you want to see the details, I suggest you play a game of fate or read a novel, where you can learn more details.