I was amazed at how much the premise of these two mangas are alike. Both stories revolve around a guy who's pretty much under the complete control of a girl as far as sexual relationships go and their girl counterpart has no shame in exploiting it. Despite both being seinen, Sundome contain much more graphic, ecchi and smutty art than Mysterious Girlfriend.
Despite having very different aesthetics, both do feature strongly atypical relationships between the two leads that is strongly founded in restricting sexual desire, as well as the release and consumption of liquid. Do note that Sundome has a very mature aesthetic, whereas Nazo no Kanojo X does not.
Unorthodox is the first word that comes to mind when describing the relationship dynamics of both series. The main male and female protagonist have a very oddball relationship that connects them on an unique interpersonal level. And while they can be over-exaggerated, it also highlights their bond in a way that is not seen in a typical relationship. Both series' settings also takes place at school where others join in the fun of their youth. Expect drama, comedy, and a whole lot of moments that will knock your seats off.
Weird main heroine in both manga. Both Urabe and Sahana got mysterious vibe to them. Main male protagonist in both manga are into weird fetishes and are submissive to their sweatharts. Only difference is that Nazo no Kanojo X is comedy and Sundome is a depressing drama with comically parts.
If 'strange' is a word on your vocabulary list when you're trying to find a series, then these two titles should definitely be on the look out for. Both series involves a female character with abnormal condition/habit. The relationship they develop with the main male protagonist puts them on oddball circumstances that often result in awkward moments. Expect peculiar comedy and plot twists that unravel themselves as the story progresses.
Both main characters kind of look the same at a distance but the difference is that in one series the girl is ugly while in the other the girl is hot (But both characters still look cute) . Both characters are kind of weird and have a rather awkward social life.
Both series also share a similar setting and are both pretty funny and amusing because of the unexpected events that happen
Taking place in a school life setting, Nazo no Kanojo X and Watamote both revolves around a main female character who is socially awkward towards others. They have trouble making friends and often misinterprets situations that leads up to controversy. Both series adapts comedy in peculiar ways with refreshing concepts molded with humor. There are also some relationship developments (more so in Nazo no Kanojo X) that influences the main characters' actions. Recommended for fans of bizarre comedy.
Both titles are about attractive but weird girls and their relationship with the guy they love. It also has the same setting and has a similar (kind of) art style and both titles are very interesting because the reader will almost always be surprised by the weird twists and you will most likely love it
Both are light-hearted and involve romance, being weird and different in their own way. Mysterious Girlfriend X is a romance oddity while The World God Only Knows is more of a comedy with romance elements.
Both are a great for a light read for entertainment.
The main characters are somewhat similar. The male lead and female lead have strange connections to each other. In MGX, Tsubaki and Urabe share each other thoughts by transferring saliva to one another, which is Mikoto's "ability." In Teiougaku, Moriguchi and Harunabara share images that Harunabara sees in her thoughts, when they come into contact with each other.
Although the two mangas have little similarities other than the obvious suspects such as the ecchiness and the highschool romance going for them but the reason I recommended each title with the other is because chances are both titles will satisfy the same target readers.
Both titles contain a lot of funny WTF! moments mixed with a lot of humor and awesome unpredictable weirdness that the readers of either titles are looking forward to