"Oh, look at that. I've been impaled."
Monochrome Week - Weapons Swap
A.K.A. - How Adam Taurus Should Have Ended
I added the top half of this illustration to add context to the bottom half, in which Weiss takes Yang's place in getting involved in the Blake-Adam conflict. It's a bit of my headcanon if Weiss and Blake stayed together during the fall of Beacon instead of splitting up - namely that they both get their abdominal scars from Adam stabbing them in his abusive, human-hating, Blake stalking, anti-Schnee rampage. Then Blake and Weiss help each other overcome the trauma Adam inflicted on them and defeat him together. This was also partially inspired by an ask answered by dashingicecream on tumblr. http://dashingicecream.tumblr.com/post/182465218712/if-you-could-rewrite-rwby-how-would-you-fit
I feel that there was lost potential by not having Weiss involved in this conflict considering the major conflict between the White Fang and the Schnee Dust Company, especially with the SDC branding revealed over Adam's left eye. Yang's involvement I can understand because of Blake brought up old experiences with Adam regarding Yang's anger when Cinder's faction set her up, and this arc helped to differentiate Yang and Adam's anger issues and aid Yang's character development. Perhaps Yang could still get caught up in this conflict as well (and maybe even retain both arms, hopefully). However, I believe there would be more significance in Weiss's involvement that would make it more meaningful and would really bolster both Blake's and her own character development. Adam's scar could open Weiss's eyes even more to the tainted legacy her father had created for her, and give her more motivation to defy and change said legacy, starting with fighting for someone she was once taught to hate. Adam would find the greatest revenge in killing one from the Schnees responsible for leaving the worst mark on him, and he'd feel even more betrayed seeing Blake fighting for said Schnee of all humans, especially if they became romantically involved. Blake would find greater solace in someone who at first distrusted faunus now fighting for her, and would readily defend her against their true antagonist.
I think that dealing the final blows with each other's weapons would be very symbolic of how much Blake and Weiss have grown together from each other, supporting one another.