Over a century ago, mankind was devoured by giant beings of unknown intelligence and origin known as Titans – creatures that eat humans alive indiscriminately and for no apparent reason. The remaining population has managed to survive the last hundred years only by building a multi-walled city capable of keeping the Titans at bay, training military recruits to patrol the perimeter and gather intelligence about their mysterious foe. Eren and Mikasa have lived a relatively peaceful life behind the city's walls, but when a massive Titan appears, smashing the outer barrier and unleashing a wave of terror, their lives are brutally changed forever...
Other than the fact that the male lead from one series reminded me of the male lead from the other, those manga don't have much else in common. But I strongly believe that this is more than enough to deserve a recommendation (at least in case of those two manga).
All Shinta wants is to find a girlfriend, and constantly falls in 'love at first sight' with his classmates. Unfortunately for the boy, none seem to reciprocate his intense feelings, and thus, he does the only thing he can think of – he visits a local shrine to hopefully have his wish granted. Much to his surprise, Shinta encounters a god at the shrine who decides to grant his wish, and the next morning, Shinta wakes up next to the lovely goddess Isana. But all wishes come at a price – it's that time of year when gods throughout the world battle it out for territory, and each deity like Isana must use a human as their champion. Now, Shinta must fight countless enemies for his newfound girlfriend, even though she doesn't seem to want to give him the time of day!
Both of those series feature a male lead who confessed to many girls without any success and who by chance finds himself a girlfriend who is (way) more than he ever bargained for. Because of this and other reasons, those two manga do feel similar, so if you liked one of them, you might like the other one as well.
Yuuhi Amamiya is a loner whose mistrust of people was instilled in him at a young age by his abusive grandfather. So when an annoying talking lizard tells the university student that he is one of twelve knights chosen to stop the gigantic "biscuit hammer" before it smashes the Earth to smithereens, Yuuhi has no inclination to rescue such an unkind world. Despite his apathy, the boy is targeted by a golem while going about his day-to-day life, and ends up teaming up with the other knights anyway. One of his new companions is Samidare Asahina, the "princess" and leader of the knights, who secretly is only trying to protect the Earth so she can destroy it herself! Entranced, Yuuhi swears eternal loyalty to this cheerful devil that promises to crush the world he despises.
Feared for his fighting prowess and his ‘Devil's Right Hand', Sawamura Seiji is one of the most well known delinquents in town. Though, behind his devil facade Seiji is merely a lonely seventeen-year-old boy who only wishes to have a steady girlfriend. Despite being rejected twenty times, Seiji gets his wish, but not in the way he thought or wanted; one morning he wakes up to find that his right hand has been replaced by a small girl! Seiji's new ‘right-hand girl' is Midori, who has loved Seiji from afar for three years; but unfortunately for her, Seiji wouldn't be caught dead dating his own hand and simply dismisses her attempts to profess her love. Now Seiji must struggle to maintain his fearsome reputation and keep Midori a secret, while she continues to hope that maybe one day her and Seiji can be a real couple.
In both Midori Days and Super Dreadnought Girl 4946 the generally unpopular with girls protagonist finds himself a girlfriend whose body size is vastly different from his own. In Super Dreadnought Girl 4946 the girl is a giant and in Midori Days the girl is tiny. Luck has it that after getting that girlfriend protagonists of both of those series suddenly do become popular with girls (now of all times). Super Dreadnought Girl 4946 relies far less on ecchi humor than Midori Days and thus seems to be the better one of those two, but still if you liked one of those two manga, the other one might be worth checking out.