Nazo no Kanojo X

Synopsis

Tsubaki decides to ask his friend, Kouhei Ueno, what he could do to advance his relationship with Urabe, though none of his advices seem to work on Urabe. When asked if they really are in a relationship or not, Urabe takes Tsubaki to an abandoned house. She tells Tsubaki to close his eyes and then she undresses, and then feeds Tsubaki her drool, explaining that their drool is a special bond that allows them to know what they are feeling. The next day, after Tsubaki has a strange dream involving Urabe, Urabe drinks some of Tsubaki's drool and somehow manages to recall his dream in great detail.

(Source: Wikipedia)