ooph360
Sero is the basic of basic. A guy in the textbook definition of 'guy'--had a girlfriend or two, regularly goes to parties, works out a bit. Everybody thinks he's cool, but nobody thinks he's interesting. He plods slowly through life, not really ever the focus of attention, not until he finally lands a spot in the esteemed UA do his friends seem to really know him... but is he just another guy there too?
On the other hand, Yuno is the complete opposite. Someone who has reached the peak of humanity-- a role model for everyone and the true meaning of extraordinary. Except she doesn't understand many things. Yuno doesn't 'get' the idea of knowing herself, so when she enters UA as a support course student she's pleasantly surprised by what she finds.