Chara and Frisk, but they've been fused together during an experiment-gone-awry, done by Alphys. Chara, however, had wanted to fuse with Frisk. She's protective and caring of her, overly so, in fact. She's aggressive, and won't hesitate to kill anyone who enters the True Lab. Frisk is much more timid and shy, and didn't want to become an Amalgamate. Chara forced herself onto Frisk as she was melting, and had fused with her. Frisk has no choice, but to listen to Chara...