Mikoto Urabe might be an anti-social loner who sleeps on her desk, carries scissors in her underwear, and laughs insanely for no apparent reason, but when Akira Tsubaki comes into contact with her saliva, he finds himself inexplicably addicted to her. And if that's not an unusual enough basis for a relationship, what's even weirder is that not only does Urabe seem to find this twisted state of affairs to be completely normal, but she already appears to have plans for her new friend! But can a girl having great expectorations for you be a good thing? Find out as Urabe puts a spittle love in Tsubaki's heart and things get REALLY bizarre as "sharing spit with a girl" takes on an entirely new meaning in the most dysfunctional bodily functional anime ever: MYSTERIOUS GIRLFRIEND X!