For new players, the friend list has a maximum of 20 friends. Once you get to player level 63, the friend limit increases at a rate of 1 per 3 levels, so that your friend limit will be 1/3 your player level (i.e. at player level 90 you will have a limit of 30). You can also mark friends as favorites, although all this seems to do is prevent you from deleting them. For each friend you can see when they last logged in, what their player level is, and a list of all the mercenaries they configured to be available to hire.
You can add friends to your list using the "search friend" option. From here you can search by either the player name or the friend ID, then send a request to add the person to your friend list. If someone sends you a friend request, it will appear in the requests tab of the friend list.
Your friend ID will be displayed on the main friend page. Your player name is what is configured under the settings section under Player Info.
Alternative Invite Options
When you do a multiplayer quest with players not on your friend list, if you have open friend spots you will be prompted after the quest to send them a friend invite. When using a mercenary from a player not on your friend list you will also be prompted to send them a friend invite. It is also possible to click on users inside the in-game chat and send them a friend request. Note that if their friend list is full they will not be able to add you.
In the receive section, you can configure what type of gifts you would like. Ideally you want to set all 3 of these to friendship coin. The other option is 10,000 Zeni, but the friendship coins are generally more valuable and can be used to exchange for items in the Friendship Coin Exchange. You can also see who has sent you gifts since you last collected them, and you can click the "Receive [Bulk]" option to receive all coins that have been sent since the last time you clicked that button.
Under this section you'll see a list of all players you have not sent a friend gift to yet for that day. You can (and should) send gifts once a day. It will not cost you anything to do so. To send gifts, press the "Send [Bulk]" button. Note that when you add a new friend, it will be 24 hours before you can send and receive gifts from them. If you don't send gifts regularly to your friends, they may remove you. There is a daily mission to send gifts to friends that gives you 10 friendship coins.
Benefits of Friendship
It's advisable to add as many friends as possible to your friend list. There are two primary advantages to having friends on your list:
- You can use the units belonging to your friends as mercenaries. Each friend can configure a list of one mercenary for each element, plus an extra mercenary of any element, which become available to hire. They get zeni from when you hire them (and you get zeni from when they hire your mercenaries) and you also get an additional leader bonus from your friend's mercenary when you use them
- You can receive gifts from your friends. Each friend can send you a friendship coin or 10,000 zeni daily (this does not cost anything to send).