>>280384095
If there's too much guilt then the Asa/Yoru will rather die than weaponize that person. That's not the scenario that Shigga has been looking for.
She's been trying to create a scenario where Asa/Yoru will feel enough desperation to weaponize Denji without feeling too guilty about it, but it's apparent that they've come to have too much affection for him.
So, most likely, her next plan is to try to create a rift between Asa and Denji, while also making it seem like the heroic thing to do from mankind's perspective, so that the guilt will be less than now.
It was never really implied that they need Asa to feel massively guilty about it. Just guilty enough.