Since Kurai went through a phase of bunking off from the academy, maybe him and Nettaiya could have once been close friends. It's up to you though dude!

As for the others... I can't imagine many of the stronger students liking Nettaiya outside of the academy...

Oh! Even better idea - maybe he pissed someone off at some stage in his school career, leading him to have an enemy. Not even someone as close as a rival; literally just someone who looks down on him for some long - forgotten past transgression... Any ideas guys?