"Mysterious Girlfriend X (謎の彼女X Nazo no Kanojo Ekkusu?) is a Japanese manga written and illustrated by Riichi Ueshiba. It was originally published as a one-shot story in 2004 before becoming a serialized comic in Kodansha's Afternoon magazine in 2006. The manga is licensed in North America by Vertical. An anime adaptation by Hoods Entertainment aired in Japan from April 7, 2012 to June 30, 2012,[1] with an original video animation episode released on August 23, 2012.
The series follows the relationship of Akira Tsubaki and Mikoto Urabe. Urabe is a transfer student who recently came to Tsubaki's school. After a series of strange events, Tsubaki finds himself addicted to Urabe's drool. Once she claims the addiction as love sickness, the relationship slowly progresses, focusing on the odd bond that comes out of the drool attachment.

As the story progresses, the relationship between the two deepens into genuine love. The manga strongly foreshadows that they will never break up, but rather will stay together for life"