God of the Abyss is the 83rd chapter of the Berserk manga series containing a one-on-one conversation between Griffith and God. It was not published in either the Japanese or translated tankōbon at Kentaro Miura's request, his reason being that he felt that the chapter gave away too much information too early in the story.
This review is nothing but spoiler on this 17 page "chapter". ~SPOILERS~ A good divergent supplement to the Berserk story line it also adds a new "Major" boss that may be the puppet master behind the entire series. I can see why Kentaro Miura didn't want to add it when he originally wrote it. The being that is that worlds possible "god" is a giant heart that has too many valves, with a ton of eyes in it's "body", damn these quotations, attached to a helix that has a whirlwind of emotions swirling around it like a hurricane. It saying that this visage is nothing but its core. It raises more questions than it answers but it does answer Griffiths' question of who it is, and what it wants. It took a few minutes to read definitely worth a few reads to just let it sink in. Nothing super existential but only to Griffith and his place in the universe.