The reason why Chise decided to "break up" with Shuji was simple. Well one of the reasons was because he had hurt her for spending the night with his former sempai (senior) when he had already agreed to meet her elsewhere. And apparently, he also did it with his former sempai. But the real reason she wanted to bring their relationship back to just being classmates was because she didn't want to hurt him. She was desperately looking for someone who would see her as a girl. And she desperately wanted her boyfriend Shuji to see that as well. She knew that he loved her and yet he was afraid of her. It was obvious that he was afraid. The way she spoke of destroying planes and taking lives was as if she had done it all her life. Example:

His eyes drifted away to a crash site while embracing her and she said: "I did that on the way home. It was easy. And they didn't even suffer. They died before they even crashed"

He was afraid of the calamity in which she said that. But from her point of view, it was really nothing. Her job as an ultimate weapon was to aid the Japanese troops by destroying the enemy. And she did that by obliterating the entire city irregardless of who was in it. Compared to the cities she had already annihilated, one plane was nothing. Besides, her boyfriend had no idea at all how much pain and grief she went through everytime she levelled a city.

Quoted: "Everytime I destroy a city, they feel no pain."
"I want to die. Can you please kill me? It hurts so much. Everytime I wake up all I see around me is dead people. And I killed them! *She then sobs for a very long time while her officer just points his rifle at her back* No! Please! No! Don't kill me! I want to live. Because I am in love. I want to live for him!"

Ok. I guess enough about She, the Ultimate Weapon. My cousin brought me to Sim Lim Square today to get me the PC which William so generously 'built' for me (PS: ayy thanks leh William. I owe you a lunch for that. Must remind me ya!). And all the way, he was telling me that he was never really in favor of me getting a new PC because I was in the army and it was a waste of money and I would be getting a laptop in 2 years and because I didn't need such a high end PC...etc. He was also lecturing me about how if I wanted to get something, I must put in effort and not expect the PC to just come flying my way. Sighz. I guess it all made sense in a way. And I could understand because if I were to get a new PC, he would be doing ALL of the work since I knew nuts about it fixing and configuring my own PC. But oh well. Its still at his house undergoing reformatting of hard disc and the type.