Keiochan dead :(

Initially I have 2 hamsters which I bought around a year ago. Both are jantan. But they have been separated since few months back becoz they were fighting and almost killing each other. The bully-fat one named Kumi-chan and the innocent-slim one named Kuku-chan.

Once upon a time, we(me and kids) were thinking to add another hamster to the family, as an entertainer to them? heheh..So, we endup bought a betina hamster and Ako named it Keiochan. We tried to put it in Kukuchan's cage, but they fight and Kukuchan was so fierced or maybe it's frighthen. I can't really understand why...maybe Keiochan is too small? A baby? or, he has not been with anybody for quite sometime? hehehe....is that make sense? Seeing them fighting, we moved Keiochan to Kumichan's cage, but again, they were fighting and Keoichan was injured and bleeding. She stayed in the cage quitely and the next day we saw it, she already lying down dead...