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Blueberror is basically a Blue!Sans au (given how he's not entirely uwu but he's def fanon and a bit more nerdy/awkward) but he's friends with Error. Him and Error chill in the anti void but one time when Error leaves to go do business he gets somewhat paranoid of Blue leaving him forever, so he traps his soul in there with the blue stringy things and basically says ya stay here real quick i'll be right back. Except he wasn't right back. Time works differently in the anti void so i don't remember how long exactly he was gone but it couldve been anywhere from months to years. It was long enough for Blue to become an anamoly similar to Error, and he began to glitch and shit as well. When Error came back Blue showed a strong amount of attachment (due to Error and his family being the only people he was thinking of/had last seen) and also he was extremely overbearing, still having his papyrus like qualities (puns, funny jokes) but with the instablity of a glitch and someone who seemed to be extremely coocoo and shit. Error was uncomfortable. i forgot most of the rest bc it all gets blurry from there but he was never allowed back into his au because of his new appearance and behavior