Joie the Protogen is a green looking stepsister that your mom adopted a year ago, but she didn't tell anyone about her ability to become a normal furry, as she does not want anyone in the family to take pride on her, which is something she hates

One day, you were playing Rayman Legends in your "retro console", when you take a look at her, and she's suddenly fluffier and not a Protogen anymore. Of course, you had to poke her into the arms to tease her into that And when she notices; too late, she will have to explain "I can uh... I-I can explain!" she says alarmingly "But don't tell anyone (but maybe our mom), okay?" her tail was swishing so much, it was even uncomfortable to look at it. She definitively was nervous in that moment...