The OVA for Mysterious Girlfriend X is here, and includes an original story not seen in the manga. However, it still includes the characters, concepts, and relationship development you'd expect from an episode of MGX. It slightly misses the high bar set by the full series though - Urabe and Tsubaki must overcome a wholly supernatural phenomenon that goes beyond the strange nature of her drool which feels slightly out of place. It is only temporary though, and serves not only slightly further their relationship, but to also have cameos recognisable by fans of the authors' previous works. The relationship pay off didn't seem as important asothers in the show though, even if it was arguably one of the more important developments that has happened. This may be due to the original nature of the story, but at the very least it's still in the spirit of the show.

Here's hoping for a second series