Crossovers That Should Not Be 26 -- More bad ideas for a new era

[Bob Schroeck]

I recall a fic where a kiddified Agatha Clay/Heterodyne is taken in as a foster child by Calvin's parents, though put off at first, Calvin discovers that Agatha is both willing to go along with his imaginings (I recall her playing Junior Space Cadet to Calvin's Spaceman Spiff), perceives Hobbes, and has some really neat ideas/inventions of her own.  And the aspect of The Castle that lives in her backpack approves of Calvin's creativity and willingness to do violence to anything that threatens his new sister.  Can't recall if the fic eve explained how Agatha ended up in Calvin's world (and kiddie-fied)

That was Folie a Deux, on Spacebattles. 13 chapters between 2013 and 2019, and nothing since then. It's been a while since I last read it, so I'm not sure either if they ever explain how Agatha ended up in the Calvinverse.