I actually made a thread about this topic a few months back.SMT x Fire Emblem. The initial concept trailer showing all the original characters got me hyped, then we got the actual game trailer 2 years later and it turned into some idol musical anime game. It's no wonder it bombed twice.
Tokyo Mirage Sessions #FE IS both a Fire Emblem and Shin Megami Tensei game, in both story and gameplay. [spoilers]
I just finished Tokyo Mirage Sessions #FE Encore the other day. I had played the original on Wii U but never finished it. I was chomping at the bit for the Switch version. Fair warning, I will be discussing some open spoiler stuff in this post, but I will try not to spoil EVERYTHING, and even...
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Bottom line: That original trailer was a bunch of jpegs that Nintendo jumped the gun on showing. We DID still get SMT x Fire Emblem, it just wasn't a "Demi-Fiend vs Marth" thing.