Tsuihou Ouji wa Dorei kara Yarinaosu - Ch. 8

[MangaDex]

 

[Salfaro]

I was kinda hoping that the twist was gonna be (rather than adamantite nullification), that he had inherited miracles from his mother, but that basically his hatred towards the empire allowed his prayers for their demise to override their prayers for their own miracles. So the reason that the Saint's healing of her son failed would be that he was praying it would fail, and then he'd just defeat her by praying for her to die, so her healing wouldn't work, not because the sword nullified it.