You can restrict communication from players registered to your block list.
You can register up to 10 players to your block list.

[Blocking Players]
If you want to block a player, open up their profile page and tap on the [Block] button.
[Unblocking Players]
You can unblock a player by opening up your block list from the [Menu] and then tapping the [Unblock] button next to the player.

Blocking a player will restrict the following:
[Both Blocked Player and Blocking Player]
・Sending chat messages
・Sending Friend requests (If they are already registered as a Friend, they will be removed from your Friend list.)
[Blocking Player Only]
・Messages sent by the blocked player will not be visible to you in the Lobby, on Quests, or in Guild Battles.