It might be fear, don't forget Thanos is an alien it since his skin is purple the color they would normally use for fear they used pink instead as it will show up better against it
It also could be because in Marvel comics Thanatos used to try and date Lady Death but she didn't feel the same and because she is one of the most powerful beings in the universe her being with Harry is really bad for his plans
Why is he blushing
It might be fear, don't forget Thanos is an alien it since his skin is purple the color they would normally use for fear they used pink instead as it will show up better against it
Ah make sense
It also could be because in Marvel comics Thanatos used to try and date Lady Death but she didn't feel the same and because she is one of the most powerful beings in the universe her being with Harry is really bad for his plans
I know that's a fic in AO3 I just remember it