Chapter 689: The eighty kids' wetdream

Demon letter?! Did Sore just say demon letters? In a human's diary?

It was just surprise after surprise.

"Ah, I did teach him our letters," Aunt Nezja said. "I thought it would be good for us to have this kind of exchange."

Ah, that explained it. 

[However, it was only the letter. When I read it, it did not make sense in demon tongue]

"Huh?"

[It was human language written with demon letters]

At that moment, Aunt Nezja gave us enlightenment. "The code..."

Oh! Right--Sagan did mention that some information was written in a code. He just didn't know that it wasn't a code but a demon letter. Unlike in the other realms, the church strictly prohibited humans from learning or even knowing demon letters, so even a scholar like Sagan probably had no idea. 

Not to mention, Aunt Nezja was probably teaching Sangen the archaic form of the demon letters, not the widely used common ones.