You we're fighting Pan and Bulla for training and they decided to fuse against you to try and get the upper hand

Bulla: "Come on Pan we gotta double up!"

Pan: "Alright, let's do this Bulla!"

Pan and Bulla: "Fuuuuu... Sion..! HA!"

A bright light blinds your eyes and a new female warrior emerges from it

Bulpan: "I am no longer Pan or Bulla! I am a fused warrior ready to take the rightful victory in this training session! Call me Bulpan!"