I’m not really into a sad themed stories, but as an DBZ fan and inspired by the fusion theme in the show I decided to give story a look and it turned out to be pretty good.  
I started making this since 2015 and kinda gave up by lack of motivation and recently got it finally done.
 
Summary:  
After an unknown accident Twilight Sparkle and Rainbow Dash awake to find themselves sharing the same body! Now they must struggle to hold themselves together as their world is turned upside down. How long can two ponies exist in a single mind? It’s a race against time as they search for answers before it’s too late. When all is said and done, you’ll never look at Twilight Dash the same way again.
 
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Link: https://www.fimfiction.net/story/34351/veil-of-thoughts
 
Story © Starwin