Rubellite was made in Earth's kindergarten. She would have been around Sapphire's height had she been able to incubate properly, but another gem emerged above her and caved in the hole Rubellite had been incubating in. Shortly after that, the kindergarten was shut down, the injectors were disabled... and that was it. She wasn't finished growing and stayed in her gemstone for a few hundred years before finally deciding to take on a physical form. She was very tiny, and was very weak at first, and preferred to stay in her hole just observing what little there was to see for a long, long time, until she became curious and started investigating around her. She created a tunnel system spanning from one side of the kindergarten to the other. She tried digging upwards once in the process of making it, but a partial collapse that almost cut off part of the system scared her into never trying to do so again. Which is unfortunate, because her current base is almost directly under the hole Amethyst came out from, and if she'd just dig up she could be free.

She's never met another gem before, but she's heard them. And it terrifies her, because she's used to the sound of rocks falling, not voices. When Amethyst, Steven, and Pearl were there in On the Run, she heard them. Every other time a Gem has been there, she's heard them. Part of her gets angry, because she feels this is her home, not theirs. And part of her is curious and wants to see what these things are.