When you're interested in other players, you can set them as a "Followed Player".
You can check out the menu by tapping on the [Followed Player] menu from the main menu (≡).
Following players allows you to whisper or send invitations to those players more conveniently, and following each other will give both characters access to view each other's equipment.
You can also block characters from the Followed Player screen.
Blocked characters cannot send you private messages or party requests.
The Followed Player list and Block list can contain up to 50 players each.