I’ve seen this panel popping up a lot at how harsh Mephisto was for quoting and twisting the late Shiro’s words to Rin like an utter douche (though he’s a demon and he’s allowed to be an asshole.)
However what no one seems to be questioning so far (which is kinda more mindblowing) is this…
How the hell was Mephisto able to quote Shiro in the first place? Those lines were said between Shiro and Rin only.
Very intimate and private.
So here’s another question to add to the enigma that is Samael/Mephisto Pheles.
Is this fabulous mofo telepathic?
Likely not, he is however fascinated by humans and has been shown to pause time and just watch them from the shadow like a creep. It could be possible that he got word that Asteroth was planning to make contact with Rin and just sort of started snooping around the monastery to see how things were going. Life is but a stage play to his fuck face.