This one stayed in my mind long enough, so I will share it.
Crossover with Ghostbusters
A summoning attempt in New York went a little... strange. The shipgirl appeared in (well, on) the Hudson River... in the middle of what she knew was a crossing of the leylines. It did not take that much time for the official to find her, thanks to her unique riging and suit. (She's wearing the Ghostbuster uniform, only white, with a proton pack on her back (a fully upgraded one with all the add-ons from Ghsotbusters: The Video Game (Realistic Versions)).
Thanks to all the ghost and other stuff shenanigans, Ecto-8 was a rather unique shipgirl. Unique enough that her spirit was summoned to another Earth in the past (for her, as she sank under the assaults of powerful ghosts and entities after several years of service). Her (few) fairies were more individuals and unique than others, with four (if it is not the only fairies she has) being the imprint left by the four original Ghostbusters. With them, mainly Dr. Egon Spengler, Dr. Ray Stantz and Dr. Peter Venkman ( by the way, he is possessive and protective of Ecto, much to her annoyance since they aren't an item), she can and may discover the truth behind the origins of the Abyssals. (I'm sure there is an explanation that will go over my head, along with all the theories that they made before discovering the truth.) Her fairies also say "Ghost!" and "Busting!" (in battle only), except when introducing themselves where they use "Ghostbusters!", instead of "Hey!". The Ghostbusters can even use their own Proton Packs to help Ecto in battle.
Her uniqueness and her exposure to psychokinetic energies made Ecto-8 much more resilient to Abyssal and Shipgirl caused damage, which started her scientists' theories on what kind of entities they were. Still, this allowed the Shipgirl to join the fight... and get quite feared for her weaponry. Her name only rose in infamy among the Abyssal when she first used the Slime Blower. Not only was it highly effective (and painful), but it was also humiliating. As it didn't work on Shipgirls, this confirmed that the Abyssal had black slime or were infected with it. Of course, the Composite Particle System was also highly effective, even more in fact, but the Slime Blower not only was used for proving a theory and clean the place of black slime, but also worked as a psychological weapon, since Abyssals (the more intelligent ones that is) (and Shipgirls) don't want to be slimed.
Potential idea: if Abyssals are corrupted Shipgirls, then Ecto-8 using the Slime Blower long enough can cleanse any of them and leaving only a slimed Shipgirl (or their equivalent if one chooses to).
How long do you think it will take until Ecto-8 form a new Ghostbusters team?
Edit: totally forgot to put this. I allow anyone who wants to use this idea, because I don't know what I would do with it.