Doc Brown found himself in Universal Studios Florida after flying across the sky in the DeLorean that he time traveled through when he suddenly noticed a bunch of Touhou girls popping up out of the void near him; given that this was 1990 he was at the spot that would eventually be the sight of the Back To The Future ride.
"Great Scott!" Doc Brown exclaimed in surprise with a stunned look of pure disbelief on his face.
"Hey isn't that scientist dude the 1 from the movie we watched?" Reimu asked with her arms folded together for her stomach growled and she let out a big loud fart. "Because he's definitely familiar!"
"Oh yeah I know him!" Marisa exclaimed happily upon going through a variety of her witch spells which ended up backfiring on her and made her farting too. "He's Doctor Emmett or something!"
Doc Brown composed himself upon shaking his head in that ever crazy scientist way. "That's my first name yes. Perhaps things in the space time continuum will be more clear if I explained myself properly...!"