The last battle between the Gotei 13 and the Quincy looked a lot like the current one, only in reverse. Yamamoto’s thirteen captains back then were vicious, savage killers who made quick work of the Quincy … yet Yamamoto wasn’t able to take Yhwach’s life.
That day of slaughter is memorialized in a painting in Yamamoto’s dojo, as seen by a young Shunsui. Yamamoto warned Shunsui that if the subject of the painting ever returned to Soul Society it would be a dark day indeed. And so it is, with Yamamoto being sliced in half by the real Yhwach after expending all his energy fighting a fake one.
With the Head Captain defeated, Yhwach orders the Stern Ritter to summon their foot soldiers to complete the slaughter of shinigami. The soldiers meet little resistance, mowing down their opponents with east and leaving Soul Society dark, burning, and drenched in blood.
It would appear Yhwach and the Quincy have had their revenge, but after being unable to simply stand by and watch countless lights of souls in Soul Society wink out, Ichigo manages to power his way out of Quilge’s prison and completes his journey through the Garganta.
The first Quincy to encounter him falls quickly by his sword, but before engaging Yhwach, Ichigo pays a visit to Kuchiki Byakuya. Before the sixth captain dies, he takes solace in knowing Rukia and Renji are still alive, and asks Ichigo for a final favor: protect Soul Society—what’s left of it, that is.
Yhwach is surprised but not totally shocked to see Ichigo before him, having defeated Quilge’s prison. It only reinforces the fact that Kurosaki is one of the five special threats that stand in the way of total victory over Soul Society. Ichigo, meanwhile, is already bloodied and battered and not in the best shape to face off against the Quincy king.
That said, he still puts up a hell of a fight, even if Yhwach is likely holding back from killing him. Their ensuing battle is nothing like the flame-wreathed inferno of Yamamoto vs. Yhwach. Things get downright 2001 trippy with the colors and patterns created by the sheer force of their attacks upon one another. But in the end, Yhwach puts his blade in Ichigo’s throat.
Confident he’s disabled but not killed Ichigo, Yhwach prepares to take him back to their realm so that he can revive him and turn him to his side, But he encounters another surprise: Ichigo is still conscious, Yhwach’s stunning strike blocked by a Quincy technique: Blut Vene.
Yhwach surmises that Ichigo’s persistent contact with Quilge’s prison when he busted himself out caused the Quincy’s spiritual pressure to mix with Ichigo’s, enabling him to unconsciously use the Blut to save himself. Yhwach takes off the kid gloves and surrounds and restrains Ichigo with rocks.
But then, just like that, he gives the order to withdraw. It isn’t a retreat, merely a break in the invasion that will be resumed again soon. The Quincy have only a limited timespan in which they are able to function outside of their realm, and that time comes sooner than Yhwach expected due to a little illusory fuckery from his brief encounter with Aizen.
Speaking of fuckery, Yhwach gives Ichigo something to chew on while heals up and awaits his return: the fact that he’s … a Quincy? Or, at least, possesses Quincy blood. It’s why Yhwach hesitates to refer to himself as Ichigo’s “enemy”—as far as he’s concerned, Ichigo is family: a prodigal son to be brought back into the fold. But something tells me Ichigo won’t be going quietly.