How do you recruit Grandmaster or Pathfinders?

20 completed pieced and then go to recruit on your suburb map. They are in there.

Throughout the game you will unlock shards of master seal shards or pathfinder seal shards, you can get them in chests (which you find in your bag) as well as other game play. You can then fuse them 20 master shards or 20 pathfinder shards to get one whole seal. You will need to collect 20 of those seals to purchase a master or finder from the recruit option under suburbs, they have several of each to choose from so have a browse to se what you like.

Once you recruit them they will become one of your retainers. Hope this helps.