User blog comment:Dangai Train/Yhwach's backstory/@comment-26420452-20131007044101

The backstory must be revealed, it's what drives the current events. Nevertheless, I don't think the Shinigami and the Quincies were ever friends. It's implied that 1000 years ago, it was the Quincies who ruled the afterlife and that the Shinigami were just a group of rogues in Soul Society. There was a war and the Shinigami won. That probably happened because the Soul King decided he had had enough with the Quincies.