This is a guide on how to recruit the Gatekeeper in Fire Emblem Warriors: Three Hopes.
The Gatekeeper is a character that gained some fan support during Three Houses, although he wasn’t playable in that game. The good news is that the Gatekeeper is playable in Three Hopes, although it will take a while before you’re able to get him into your party.
In order to get the Gatekeeper to join your party, you need to have completed the game twice, while using New Game Plus. You will be able to get him across all routes the same, but it largely depends on which route you took on your first two playthroughs. Yes, those initial two playthroughs will need to be done with two separate Houses. For example, if you went with Scarlet Blaze on your first playthrough, your second playthrough on New Game Plus cannot be Scarlet Blaze again. It will need to be a different House.
That means you would either need to do Golden Wildfire or Azure Gleam on the second playthrough of the game (New Game Plus). Then, once you reach the end of your second playthrough and start up the third, simply pick the only House left over for the second New Game Plus. While you go through that third route, you will be able to speak with the Gatekeeper from Chapter 5 onwards until he joins you. The Gatekeeper is located, well, by the gate of your base.