Below is my little analysis on the way Sasame thinks and why he choose to act the way he did, hopefully to give you a good understanding of Sasame.

At first glance, Sasame is exactly what you'd think he would be like. He has a sweet and caring face, he always wears a smile, he's intelligent, understanding, mature, and he's a pro at giving advice. He knows Hayate inside and out, as Hayate is his closest friend. Thus, to have the courage and will to fight him and possibly kill him takes a lot out of him. If you were to look at his points of view, you would see that Sasame has gone through much pain. He loved Takako but could not be with her. He only stood by and watched as Takako fell in love with his closest friend and then have her heart broken by him. How easy would it have been for Sasame to hate Hayate for all he's done to Takako? Yet he stood by him loyally and continued to carry out his missions. He was never visible to Takako, and he chose not to tell Takako his feelings because he thought it would bring her more pain. When the Knights sealed her away, Sasame remained true to his duties as a Liefe Knight and sealed his loved one away. He was torn between doing the 'right' thing as a Knight and seal Saihi away and abandoning all that he's stood for to be with the one that he truely loved. Perhaps it is forbidden for a Knight to be with Saihi, but some feelings cannot be suppressed no matter how much you try. Love can bring out the best and worst in people. If the love is strong enough, good and evil, right and wrong, might not matter anymore. To declare that anyone's love is wrong, or that it is wrong to love a certain person, that in itself is a wrong statement. This is the reason Sasame did what he did...

As a Knight of Darkness, Sasame knew Saihi was simply using him, but he let her use him, so long as she is by his side. But even while he was working for evil, he knew exactly what he was doing. But he did it willingly, because doing it would make Saihi happy, and that's what he wants the most. While he was with Saihi, watching the world come to an end, he hinted that no one will be able to be hurt or suffer anymore...or love. He was trying to make Saihi realize what she would lose, love and happiness. When Saihi told him to kill Himeno and Hayate, one can see sadness in his eyes, partly out of seeing Takako emotionally hurt and partly because Himeno and Hayate are both good friends of his. Himeno made Sasame realize that in order to save Takako, he cannot go and help her end the world. He must understand her feelings, that she was scared and suffering. With his last breathes before dying, Sasame told Takako to throw away her hatred and end her suffering. He admitted that he failed to understand Mawata's feelings and took advantage of her. He felt that even his death couldn't repay for all that he's done, but at least he could now be Takako's knight... *_* All of his actions finally moved Takako and she wished for anything to bring him back. Through all of Sasame's efforts, he was finally able to experience true happiness and love with the one that he's sacrificed many things for. Sasame was not only able to bring Takako back, but he also healed her heart of suffering and pain and replaced it with love from his heart. To answer the questions, why did he abandon Himeno and the Liefe Knights? Why did he go from returning liefe and protecting liefe to stealing it? Why did he attempt to kill Hayate several times as well as Himeno? Why betray your fellow knights and throw away the respect they've given you? Why take advantage of an innocent child's feelings? Why risk your life to save someone? Sasame did what he did out of love, to gain a love that he's never had. He believed that the fate that God had given him was not to look on in pain, to see his loved one be with someone else. He pursued his dreams and goals, and in the end, he was finally able to be Takako's true knight.