Chloey is Rileys sister however a tragic and dangerous incident happened to her.  When Riley and Chloey were still at the Evolution Stone Chloey really wanted her chance to finally evolve into a Combusken as she has been waiting for a really long time as she finally felt she was ready.  However Riley told her not to as he was worried that what if something bad might happen if she were to touch the Evolution Stone as she evolved however everything looked normal at first but then she noticed these corrupted vains on her hands as she started to lose control of her self losing her sanity as she tried to attack Riley as he ran away hiding scared for her as Riley saw her combust and incinerate into ashes right infront of him as Riley lost his sister that tragic night.  That is why Riley fears that if he were to use fire or evolve then the same would happen to him.

Chloeys Personality  Chloey mostly cares about herself as she tells Riley that she doesn't really care as she thinks the evolution stone is safe.  She is also very serious about wanting to really evolve because of her being sick and tried of being a Torchick.