How in the world is Light Yagami a Pisces?? lol?

Well you are right about Virgo's always analyzing things and always thinking about things under the surface. However To answer your question, 1) you should also know that not everyone matches there sign, they are many different things that come into play when dealing with the stars, but Pisces are clever, deceitful, manipulative, self centered, they can lose touch with reality and temperamental. Really I can see alot of those in Light, maybe not all of them and BTW these are just the Neg qualities too.