In 2013 Nintendo announced a collaboration with Atlus to create a crossover between Shin Megami Tensei and Fire Emblem for Wii U. The debut trailer was a teaser with artwork of main characters from both franchises with very little information besides being a Wii U RPG. There were worries that the game had become vaporware, with no additional information or actual gameplay footage. Today, during the April 1st Nintendo Direct, Nintendo finally revealed the game is alive and well with a new trailer.
The game is tentatively titled Shin Megami Tensei And Fire Emblem in the West, but the Japanese trailer has the title Genei Ibunroku #FE. According to Gematsu, the game is scheduled for release Winter 2015 in Japan while a Western release is looking to be sometime in 2016.
Judging from the visuals and music, the game appears to take more after Persona than mainline Shin Megami Tensei. According to NoA Director of Product Marketing Bill Trinen during the Nintendo Direct, the game’s premise is about the main characters as they go to school and travel around the city while discovering their world co-exists with a secret world of fantasy featuring Fire Emblem characters. The battles feature a more fantasy twist compared to other Shin Megami Tensei and Persona games. These scenes are too brief to describe, but the HUD display shows the turn order for allies and enemies. I am not sure of any other gameplay mechanic, or how the main characters interact with Fire Emblem characters.
You can check out the official Japanese site here.