This is an Alternate Universe of the show Steven Universe. In this universe, Rose and Greg conceive Twins. Rose realizes she can only give her Gem to one of the babies and begins to grieve over this. Pearl notices this grief and, knowing she’ll lose Rose either way, decides to give her Gem to one of the babies to make Rose happy.
The twins are born as a boy and a girl named Steven and Nora. Neither Pearl nor Rose planned on which baby got which Gem, so it was just coincidence that Steven got Rose’s Gem and Nora got Pearl’s.