It's most likely Yhwach. That pattern appears on Ichigo whenever Yhwach is doing his magical quincy powers on him. It happened when Ichigo cut the soul king.
Ichigo's blut vene is different than Yhwach's. It's rather called Plot Vene.
If the Attacks werent enough to kill uryuu, they wouldnt be enough to kill Haschwald, who would then chuck them back x2.
Right but he could still reverse back for the time being. Also if an attack that was enough to kill him hits him then he would die instantly wouldn't he? That would leave no time for him to throw it back which makes Haschwalth victorious, why didn't he just do that?
Well, both their powers work by reflecting attacks. Haschwalth doubles any damage he reflects. If Uryu lands an attack (haha) that's strong enough to almost kill Haschwalth, Haschwalth can reflect it twice as strong and kill Uryu. If Uryu takes an attack strong enough to almost kill him, he can give it haschwalth, who then gives it back, twice as strong, and kills Uryu anyway. Either way, Haschwalth is the only possible winner here.
Rukia and Renji will probably show up soon to save them. Not sure what they are going to do against the Almighty though.
Uryu's power works by reversing what has happened two different objects/people. Shunsui's power means any damage he takes is also taken by his opponent. Significant difference is that Shunsui's is a passive effect, while Uryu has to activate his power. Also, Uryu should be able to change things other than damage, since it's supposed to be altering the past.
