Blue Star is the daughter of Rainbow Dash and Lightning Storm and the younger twin. She has her mother’s blue coat, but her father’s blue eyes and yellow mane and tail. She’s more athletic than Thunder and can do a sonic boom more easily than he can as well as fly faster than him. Blue Star inherited most of her personality from her mother, thus she’s just as loyal, competitive, brash, and mischievous as she is. Blue’s also great at sports and is a black-belt in Karate. She can even control the weather just as easily as Rainbow can. Despite all this, she hates to lose just like her mother does and is allergic to peanuts as she’ll swell up upon touching one. She’s great friends with Applejack’s daughter, Golden Apple, despite their competitive relationship. She even idolizes Scootaloo, much how the orange pegasus idolized Rainbow Dash.
Relationship with Rainbow Dash's human counterpart
Blue Star along with Thunder Spectrum and Sunbeam were good friends with their Mother's Human Counterpart because she's a lot like her.