@G** of delulu well all of that was just clearly explained in this chapter... they just said "that day" was when he dueled the heavenly demon and they made an alliance to go after the H** organization, that was when he disappeared 30 years ago and they had been fighting together since. The beginning of story is where he says the heavenly demon ended up being betrayed by his subordinates and marks the end of the 30 year period, you might wanna go work on your reading comprehension.