Quote from strixflash
According to Chapter 220[/url], Rai was forced to use his powers because of some incident. But from the talks between Gejutel & Franky[/url] and the way Previous Lord and Current Lord said it, it becomes clear that no major/minor incident took place 820 years ago.
According to them Rai just disappeared wit ...
How about Rai was placed in a situation where he couldnt attack or kill the people that threatend him? Like you said maybe they involved humans. I dont think there was any battle, but Rai was blackmailed to come to a place, and had no choice but to enter into a deep sleep for 820 years. But it's hard to say anything at this point, a theory like Rai got bored and decided to sleep for a while is just as legit as everything else we have said.