Yhwach is the first Quincy, so he's like the arch father of the entire Quincy clan. He pretty much is something like Ichigo's great-great-great-great-great etc. grandfather. He had children (whether naturally with another person or somehow created them with an alternative method as Yhawch had the ability to place his power into other people) and those children then had children and they then had again children etc. This is resulted in different Quincy branches and families, however each new Quincy received a part of Yhwach's power and when that Quincy died, that power returned to Yhwach after having been life-long nurtured. To Quincy are practically livestock and the power in Ichigo is Zangetsu. The latter tried to keep Ichigo from harm as much as possible, but at the same time tried to suppress his Shinigami powers. He eventually stopped doing that when Ichigo forged his own Zanpaktou and thus actually rebelled against himself as he chose Ichigo over Yhwach.
Don't you know it's against the rules of Shounen Manga to lead a fight with your ultimate technique? Otherwise Ichigo would already be in Bankai, firing Getsuga Juujishou's.
Never going to fire a Cero. It's just a Doom Lazor, he allready has Getsuga for that.
