For the time being, my sister and I cannot be online at the same time, however we have two separate accounts, two separate copies of the game. I would like to befriend her character so that we can at least exchange items and mail. However whenever we try to send a friend request to each other we're given a "cannot locate character with that name" message.

Does this mean it is impossible to befriend an offline character or is there some other method or solution? Thank you for your time and answers, they are very much appreciated!