The RPG is due to release in Japan on PS4 at some point in 2019, but game director Tetsuya Fukuhara has told Famitsu (translation via RPG Site), that he wants to bring the game to Steam too. Cygames were already planning localised versions of the game in the West.
Granblue Fantasy Relink will be set in the same universe as 2014 mobile RPG Granblue Fantasy, which proved hugely popular in Japan, but the story will take place in a different time period. You'll be able to play it in co-op with up to four players or solo.
You can watch some newly released gameplay footage above.
It's no huge surprise that a Steam release could be on the cards: Platinum has said in the past that it wants all its games to end up on PC but that it "depends on the publisher"—and for now, Cygames seems to be on board.