As revealed by Masahiro Sakurai himself, Byleth From Fire Emblem Three Houses will be the next DLC fighter for Super Smash Bros. Ultimate.
You can check out the whole hero reveal here:
Byleth will feature both male and female counterparts and their fighting mechanics will feature the Relic Weapons Aymr, Areadbhar, and Failnaught from the Fire Emblem Three Houses game. The level included will also look to feature certain characters from the game like Edelgard and others.
Byleth will join Smash on January 28 and is sold separately for $5.99 or via the whole Challenger pack.