Fly/Unfly semi infinite

sentinel

#1

launch, sj., sj.[lp, lk XX ff], (f.[lk, hp XX uf], uf.[lk XX ff]) repeat circle brackets

okay I was just wondering what the deal was with this combo when you unfly after the lk, hp part. I always try to put in the lk after the unfly and nothing comes out. Does it have to be done in the corner and does the lk kick actually hit them? I dont understand what has to be done with the unfly lk part. Thanks