Talk:Grimm/@comment-124.189.50.21-20130818101027/@comment-4010415-20130830120342

It actually happens fairly early on in the series, and he's not quite possessed by a "demon." I'll try to make this brief while keeping it from being too confusing.

Hollows, the "demons" in Bleach, are created a number of ways. Whatever way that happens, it pretty much results in the same thing: A soul's soul chain becomes broken in a way that it's separated from the soul's chest or breaks down/degrades, leaving a big gaping hole in their chest.

Now, in the first season, Ichigo (the main character) meets a soul reaper named Rukia who becomes injured fighting a Hollow that's trying to kill Ichigo's family. He's always been able to see souls, blablablah, she lends him her power, thus making him a substitute soul reaper (human who can turn into a soul reaper). Blablablah, stuff happens, this one guy agrees to help Ichigo actually complete the transformation into a substitute soul reaper. However... here's the fun part... The guy cuts his soul chain, and he has to escape a pit before it devolves into a hole in his chest. In a nutshell, he failed, but only kinda. At the last second, he harnessed his power, thus causing the creation of an "inner Hollow" as fans call it.