Guarding Spirits plays are critical to Sera's overall gameplay as they are game-changing, so much so that Sera has some trouble with summoners that can circumvent this event.  It creates big turns, whether you are on offense or defense. If you have your units well positioned to take advantage of this, Guarding Spirits can make your opponent's turn very poor and creating such a scenario is one of the ways for Sera to get an economic lead. Remember that it only works on commons though, so it’s not altogether easy to set up, but it is always worth the necessary effort.