When Steven gets wind of Gem Fusion, all he wanted to do was see Amethyst and Pearl turn into a giant woman. This was easier said than done because those two barely share anything in common! To achieve a successful fusion, two or more Gems need to have the proper wavelength to sync up. Amethyst's sloppy nature goes against Pearl's orderly structure, so a fusion between them sounded impossible! That's never stopped Steven before and Garnet knew it; she ordered him to tag along with Pearl and Amethyst on a mission to retrieve the Heaven Beetle. She correctly predicted that Steven's compassion would act as an unintended mediator between the two.
Steven spends nearly the entire mission trying to get Amethyst and Pearl to fuse, but neither of them were willing to touch each other with a ten-foot pole. Not even a giant corrupted Gem Bird was enough despite the extra firepower Opal would have provided, though not for lack of trying! They finally became Opal when the Gem Bird swallowed Steven. They may get on each other's nerves, but their love for Steven is unparalled. Opal took down the Bird Gem and saved Steven.
Opal's personality is a bit of a mystery, though she seems to carry an air of serenity around her. With Pearl's straightforward mindset and Amethyst's carefree lifestyle, Opal is a calm, reassured Gem. The only problem with her? She forgets things easily! Good thing Steven retrieved the Heaven Beetle when she didn't!