Prior to every stage, you can choose to bring an ally player with you. You should constantly do this as it makes you good friend points. After you beat the level, you can then send out a buddy demand to the player you allied with. Having fun with that player once more after you end up being buddies webs you much more good friend points!

Good friend points are necessary as you can use them to use the Friend Point Summon, which is the only way to obtain new characters besides the Dragon Stone Summon.