Elaina is Saya's crush. No doubt. The anime is very clear about this and even uses it for humour development. But Saya is, at least, someone very special to Elaina too.
In the last episode, we can see that Elaina not only ACCEPT Saya's present (the matching pendant) but she USES IT all the time.
When Saya investigates about that kingdom where nobody can lie, Elaina helps her without she even ask. Taking in account how narcissistic Elaina is, and how she's careful about being involved with something, that is very interesting.
I liked this story. Nekomura is one of my favorites. YES, this is a little fucked up but I kinda liked the way it happens. The kouhai really loves her and gets pissed hearing about her past relationships and well... really "marked" her girlfriend.
Nekomura's mostly works are gentle and heartwarming but you can see she like some little dark details here and there.