dyku is the term used to describe those denizens who were at one time ku students. Under normal circumstances a ku student will progress from initiate to infinite, however in many cases the student will never reach the level of an infinite and end up reaching their full potential at some arbitrary grade. Naturally this leads to a certain level of disillusionment for some students, especially those who never make it above 3rd grade. It's common for such people to abandon the ku and either go into seclusion, or to join a dyku community.
In some rare cases a prospective infinite, specifically a ku student of the 8th grade will fail to graduate the final challenge, and yet they will survive. This puts them in a very socially awkward situation. Almost always such individuals will abandon their identities and join a dyku community. Some will live there for a very long time before attempting the challenge again. Others will simply live out the rest of their lives as dyku.
Something interesting to note, dyku are not exclusively less powerful than ku students. It all depends on the collective genius of each dyku community. In some cases there may be several 8th grade ku students in a community, it's not unheard of for these talented people to combine their knowledge and develop unique sects of martial arts and existential techniques. Sometimes those who join the dyku for a time actually emerge far more powerful than they ever would have become assuming that they had simply become infinite. Certainly they learn a great deal among the dyku.
Incidentally, and somewhat rarely, at times a powerful infinite or ku student will temporarily go into hiding among the dyku. It is ideal cover due to the informality and openness of the community. From a cultural perspective there is a kind of intimacy and comradery experienced among the dyku that is quite a departure from the exceedingly (and sometimes stifling) strictures and formality of scholastic life.