yep

Gameboard.ShogiUI.Sockets/Models/SessionMetadata.cs

@@ -7,7 +7,7 @@
   {
     public string Name { get; }
     public string Player1 { get; }
-    public string? Player2 { get; }
+    public string? Player2 { get; private set; }
     public bool IsPrivate { get; }
 
     public SessionMetadata(string name, bool isPrivate, string player1, string? player2)
@@ -25,6 +25,11 @@
       Player2 = sessionModel.Player2;
     }
 
-    public ServiceModels.Socket.Types.Game ToServiceModel() => new(Name, Player1, Player2);
+    public void SetPlayer2(string playerName)
+    {
+      Player2 = playerName;
+    }
+
+    public ServiceModels.Types.Game ToServiceModel() => new(Name, Player1, Player2);
   }
 }