As he followed Katherin into the library, Kyo looked around for a glimpse of the demon lord, but saw only Wrath's host approaching the door. How curious... 
Another quick look around confirmed no other visible presence, but also revealed an empty teacup on a table. Unless the other boy had been having tea, that probably was evidence of the one they had just missed. Unless he was wrong and just couldn't see Death. Could he see demon lords without hosts? He wasn't sure.