Well, it depends on the magic, if it is one that affects anything they are touching, such as their clothing, then it could affect the sperm as well, and you won't get the Belle effect. Also depends on if you are shrunk, or they are grown. If you are shrunk, then anything not part of you when you regrow, might not be affected. Depends on how the magic is setup.Well, it's either the fairy gets shot across the room or she simply goes "Pop!" I suppose it'd be one way of trying to convince the MC that shooting your load in every girl you fuck may not always be the best choice.
I'm just waiting for Maria to ask Ashley if she could borrow one of the fairies to use as a dildo.