Syl and Rock

[Hen she/her]

So i've always been confused about how Rock sees Syl? Does he have a connection to her through the spiritual realm, or is it because he's a Horneater, and if that the case can all Horneaters see spren even when the spren don't show themselves? Is it because of the nature of the Horneater peaks? 

[Quantus he/him]

It's a Horneater thing.  Some (but not all) of them have the ability to see spren even when the spren are not trying to be seen.  They call such people alaii'iku.  We assume this is a result of the fact that Horneaters as a race have Singer heritage.