Click flag and bring a box of tissues.
Chara was the first human to fall into the underground. She was a good person, and made friends with Asriel, Toriel and Asgore. When she learned that they needed 7 (I think) huan souls, (I'm doing this by memory, I haven't played undertale in a while ;-;) She ate the golden flowers that were poisonous to the humans AND the monsters. She became deadly sick, and before she died, she asked Asriel to take her to the golden flowers where her town was. The humans thought that Asriel had killed her, and they killed him. There souls combined, and they were sent to somewhere (I don't remember where. ;-;) She went insane slowly afterwards because of their combined souls. ()
