Nazo no Kanojo X

Synopsis

Ayuko decides to have her lunch next to Urabe, much to everyone's surprise. As Urabe gets a scrape during PE the next day, Ayuko takes her to the nurse's office to treat it. After sharing a drink with her, Ayuko discovers she suddenly has the same injury as Urabe. They soon deduce that Urabe's drool can also transfer injuries, showing Ayuko has a similar connection to her as Tsubaki does. Ayuko mentions how she became fascinated by Urabe after seeing her with Tsubaki, but Mikoto rejects her offer of becoming friends. The next day, Ayuko feeds some of her drool to Urabe, deducing from her reaction to its sweet taste that she hasn't kissed Tsubaki yet. Afterwards, Urabe and Ayuko begin a daily routine of having lunch together.

(Source: Wikipedia)