User blog comment:CrystalDeemo/Manga - Chapter 21/@comment-25942629-20150217204433

I think it's too late for chapter 21. You can read chapters 28-30 on the magazine website, but you have to pay 99 cents per magazine issue since you're not a subscriber. Subscribing drops the issues to like 55 cents each afterward or something: http://shonenjump.viz.com/

The site ShadowRyu Kei listed steals its chapters from the magazine. The image quality has dropped a little, and the double spreads got broken up, but the chapters are the same.