Folgers Crossover

We've replaced Akane Kasuga from Kimagure Orange Road with Akane Tendo from Ranma ½. Let's see who notices.

One of the more... unusual methods with which a Fan Fiction author can choose to implement a Crossover—rather than have the casts of two different shows meet, just swap a character from one with a character from the other and let hilarity ensue. It can be a physical transposition, or a purely mental exchange—and for extra bonus fun and maximum initial confusion, have the characters share the same first name. Or ~~worse~~ better, be the same character from two different continuities.

The result is often a Trapped in Another World story, in which both casts may find themselves working to return the visitor to their own world/timeline/universe and get their missing compatriate back.

Very often played for laughs when the characters involved have radically different personalities.

The trope name comes from an Advertising campaign for Folgers instant coffee from the 1970s and 1980s which took the viewer inside various gourmet restaurants while a voice-over whispered, "We are here at (name of four-star restaurant), where we've secretly replaced the fine coffee they usually serve with Folgers Crystals. Let's see if anyone can tell the difference!"

Sub-Trope of Fusion Fic.

Not to be confused with a Doppelganger Crossover.

Examples of Folgers Crossover include:

Anime and Manga

The page quote refers to an actual fic entitled A.K.A. Akane-Chan?, written in 1993 by Jeff Yang, which may be the Ur Example of the trope. In it, Akane Kasuga and Akane Tendo swap minds (and worlds), and the lesbian Kasuga gets a crush on female!Ranma, without knowing anything about his intergender condition.
Gregg Landsman's Nobody Dies includes an extended sequence where the canon versions of Asuka and Shinji change places for several chapters with their counterparts from the world of the fanfic.
Played with in Mithril Moth's Fire in the Water, a Ranma ½/Magic Knight Rayearth crossover in which Ranma's girl form is the body of Hikaru Shidou, who drowned in at Jusenkyou a thousand years earlier thanks to Time Travel shenanigans—and Hikaru's spirit begins possessing Ranma's body.
In the Hands of a Real Hero by A. Amishi tells the (incomplete) story of what happens when a freak accident exchanges Kazuki Yotsuga and Zinv (from Parallel Trouble Adventure Dual) with Shinji Ikari and Evangelion Unit 01 (from Neon Genesis Evangelion).

Web Original

Offering up an improbable crossover in the style of the Folgers commercial quoted above is something of a running game in the various "Crossovers That Must Not Be" threads at the Drunkard's Walk Forums "Other People's Fanfiction" board. Some examples:

We've secretly replaced Charlie and the Chocolate Factory's Mike Teavee with ReBoot's Mike the TV. Did anyone notice?
We've replaced Bella Swan with Bellatrix leStrange. Let's see who doesn't notice.
We've replaced Bella Swan with Elizabeth Swann. Hijinks ensue, and all the rum is gone for some reason.
We've replaced Moose from Archie with Mousse from Ranma ½ -- let's see how much property damage ensues!
We've secretly replaced Spike from Cowboy Bebop with Spike from Buffy the Vampire Slayer, who we've replaced with Spike from My Little Pony: Friendship Is Magic, who we've replaced with Spike from Transformers, who we've replaced with Spike from Degrassi Junior High, and so on...