Button is a Ruby from the Off-Colors, often fused with Lavi to form Rhodonite.
Appearance
She looks like most other Rubies, with her gemstone located where her belly button would be, hense her name.
Personality
Button is often shown to be rather frightful to most situations, much like her close friend Lavi. Comparing her to Lavi however, she is presented as being less cowardly and more shy. This is shown in her appearances as she isn't as willing to share her concerns as prominently as her friend does.
History
Button and Lavi both once belonged to a Morganite on Homeworld, but upon being found to like Fusion, she and Lavi were replaced and they were forced to flee, joining the Off-Colors for over six thousand years.
Season 6
She first appears unwillingly when she and Lavi unfused alongside Sapphire and Ruby when they were dropped into Discord's dimension.
This happens again when Rhodonite was kidnapped and held hostage by White Diamond in her Space Station.
My Little Universe II
Button reappears when Rhodonite is forced apart by Leviathan's henchmen, her being the first to flee. However, she had to return and get Lavi out, as Lavi was frozen in fear. That night, with Rhodonite being effected prior by insults of her fear, Buttons gets the ideas that if she and Lavi faced Leviathan and saved Yellow Pearl, then they'll never be scared of anything else ever again. She and Lavi were saved later on in their escape by Jasper.