Board Thread:Questions and Answers/@comment-9826910-20130618064245/@comment-11129263-20130621234212

aizen only says that as an assumption to how he was able to physically dominate him and push him to the secluded mountainous area. then ichigo performs such feats as stopping that swing of his sword and breaking stuff as they clash swords, which later ichigo says is his power not aizens. both of those suggest he still has heaps of reiatsu. aizen is also pretty angry and arrogant at that stage so his judgment probably isnt as good as usual and ichigo says a bunch of times that aizen cant understand what he's become. also, when ichi is starting up some sweet mugetsu action, aizen has that little self speech about his power and how people couldn't feel his reiatsu until he dropped it to their level and all that.