You attempt to expel wind out of your mouth but lack the breath to blow out any. You’re using your mouth and trying to blow out some air, but you are failing to do so.
You silly fool (ふ), the reason you couldn’t blow any air out of your mouth is because your hand was over it. You can’t blow air out that way. You silly fool, you.
Currently there are no similar looking kanji which exist in the WaniKani learning system