In a livestream today, Cygames announced that Granblue Fantasy is receiving two collaborations with Detective Conan, and Persona 5.
The collaboration will take place in April 2018, and will feature Conan as a playable unit (CV: Minami Takayama).
Meanwhile, the Persona 5 collaboration will take place in June 2018, and so far Joker has been confirmed as a new character.
Here is the link to the full livestream (with the collaboration announcement starting around the 3:11:27 mark).
Granblue Fantasy is available for iOS and Android.