srb2 css art for the rosybug duo!! more info about what their deal is under the cut for those interested
in essence rosybug is a plural allegory via possession inspired by a short-lived glitch. the au was actually made as an srb2 mod first and the designs and lore came later
during amy's capture in sonic cd, metal sonic took her to a few special stages on the way to eggman in search of time stones. during one of these, she encountered an injured fishbird, which wound up letting itself be absorbed into her as a last-ditch survival effort. amy, already having plenty on her mind what with the whole kidnapping in progress, chocked it up to standard special zone weirdness and tried not to think too much of it
her ability to not think much of it eventually ran out around the time of sonic the fighters, when she first made direct contact with a chaos emerald. the radiation from the emerald brought the fishbird's consciousness out of the dormancy she had been in and put her in control of the body in place of amy, who instead takes the form of the little pink-and-white ghost in the drawing
after all the death egg ii craziness is over, the fishbird is still in control of amy's body, which is kind of distressing for everyone involved. at first, amy's friends are in favor of fully exorcising the fishbird, but after amy convinces them to fully hear out the fishbird's side of the story, they agree that it would be rude to kick her out, since she has nowhere to go. she sacrificed her body and memories and merged with amy's mind just to survive. amy finally decides to do both the fishbird and the poor narrator a favor and gives her the name rosy so i can finally stop using the word fishbird so much!
knuckles hesitantly decides to take rosy to the master emerald, since anything a chaos emerald can do, the master emerald can undo. he channels its power to grant amy and rosy the ability to alternate control over their body at will. they continue in this state for the rest of the series
as for their dynamic: amy is the same as always at heart, but with rosy encouraging her, she might somehow be even more impulsive than her canon self. that said, her most frequent impulses are "helping people or putting herself in a position to do so by taking risks that she is quickly finding herself more capable of handling than previously thought" (net positive pretty much every time) and "being affectionate toward someone who is annoyed by but generally tolerant of affection" (slightly grating at worst and would stop very quickly if it became a genuine problem) so this is less of an issue and more of a quirk
rosy herself lacks amy's tact, but she shares every bit of her compassion, especially for her friends. she likes giving people nicknames - her name came from a nickname for her headmate, after all! while she's fond of yapping, she likes to show her affection through action, and likes to seek practical solutions (i.e. hitting people who are mean to her friends over the head with a big hammer) when applicable. rosy also has a crush on sonic, which causes conflict between her and amy at first, but rosy eventually decides to put her own crush aside and play matchmaker for amy instead. she is not very successful in this regard since sonic is still aroace but amy appreciates the attempt
