User blog comment:B214/LN spoilers/@comment-27702036-20160130050143/@comment-24742995-20160131162917

The world limits the amount of potential by permitting only a limited amount of things people can do, just as much magical energy you're given upon birth(Edelweiss said that, the magical energy is the power to change the world). Ikki reached the limit of his potential that he is allowed in the world, and thus cannot advance further and is chained down by its force and started losing(it appears that only Ikki can see those chains). Ikki broke those chains out of his will because he wants to keep on being the person Stella looks up to, and broke the chains, and his magic capacity was expanded as a result, allowing him to use Ittou Rasetsu right even though he just used Ittou Shura earlier. Edelweiss commented that he won't be protected by the world too as a result, becoming someone who isn't bound by fate, but someone who can rewrite this world. That's basically all the info for volume 9, and from that we can understand that Ikki now has a somewhat larger magical capacity(although probably still terribly low at this point), and he IS still allowed to become "stronger"(not necessarily magic-wise though, perhaps his techniques will become even more insane, too little info to speculate on).