Board Thread:General Discussion/@comment-98.199.71.190-20140223181130/@comment-24088226-20140223182526

Area bosses and Archwitches seem to have a bonus to raising friendship, so either farm 1-1 since you run into an area boss every 4 steps or if your AWK team is strong enough to win with only 4 cards, put the card in question on your AWK team.

Or don't bother. If you use a card, the friendship will get maxed eventually, and if you don't use the card +5% atk/def doesn't matter.