Donnie has long given up on April and April and Casey are in an establised relationship, Though Donnie still gets a little jealous (sometimes)
Parallel universe: April and Casey are in an established relationship and are pining after Donnie who couldn't care less but he wished they would stop flirting with him while in the middle of battle (mostly Casey as April would be more focused)
Someting happens to bring these parrallel universes togeter in the heat of battle and all of the charaters from the paralle univere as well as the original one must team up.
If you can't tell yet who my favorite character is...:)
Disclaimer: I own nothing but the ideas witch are up for grabs. This is purely fanfiction I make no profit from any of this, like the picture it's not mine either, I found it on Tumblr you should go check the artist out they posted on capritelloweek tumbler page.