Perhaps the reason why rust looked like the g** must be because of the novel she was reading before dying where rust was practically mysterious and his face still wasn't shown so world(novel) must have filled the gaps with what information they alrrady have based on her(mc) which is basically copying the face of the g**. Just my speculation though.
Bl:
https://mangabuddy.com/manga-list/112869
Action - Fantasy:
https://mangab