Fulimura-kun Mates and Choku have one thing in common, both of those manga feature a perverted girl with (quite) a few loose screws. In both cases it's really hilarious (though Eri is more awesome). If you liked one of those manga, you have to check the other one as well.
In both Koharu no Hibi and Choku! the protagonist finds himself a girlfriend who is a major nutcase. OK, thats not exactly true (I'm referring to the first part of previous sentence, the second one is very true) it's not like the protagonist in any of those series was searching for a girlfriend, it was the other way around. Kouharu no Hibi takes a more serious approach and can be scary and disturbing at times, on the other hand Choku! is a comedy. If you though that Kouharu no Hibi is too serious, you should try reading Choku!, on the other hand if you want to read something with a more serious approach to the loony girlfriend subject than Choku!, then Kouharu no Hibi might be what you are looking for.
A strange new transfer student joins Akira Tsubaki's class - her name is Mikoto Urabe and she has the habit of hiding her face behind her hair and falling asleep during class. One afternoon, when Akira goes to fetch his bag from the classroom, he finds Mikoto sleeping alone at her desk. She wakes up and makes her exit, but leaves behind some of her own drool on the desk. Without thinking, Akira tastes the drool... and is surprised to find it has a sweet, delicious flavour! A few days later, and Akira mysteriously comes down with a high fever; he's confused as to what is wrong with him until Mikoto visits him and tells him he's addicted to her drool and is suffering from withdrawal symptoms. From now on, Akira will need a regular top-up of Mikoto's saliva or else he'll fall ill - but maybe this isn't such a terrible thing, considering that Akira is falling for Mikoto...
Choku! and Mysterious Girlfriend X have one thing in common. You can probably guess what it is yourself: mysterious girlfriends. MGX is really bizarre, on the other hand Choku! tries to be more like a comedy. Anyway, if you liked one of those two manga, odds are you will like the other one as well.
Both of those manga feature a similar perverted\possessive girl as a female lead and both of the girls have very little common sense. Because of that and also because of the fact that both series are comedies, it's highly probable that you will like one, if you liked the other.