Yamaguchi Kumiko is next in line to be the boss of the Kuroda Ikka yakuza clan due to her parents' death. However, fresh out of college, Kumiko decides to pursue her lifelong dream of being a teacher. Now hired as a mathematics teacher at an all-boys school, Kumiko must hide her true identity. She's assigned to class 3D, inhabited by the worst of the worst delinquents. Popularly called "Yankumi" by her students, she tries her best to gain the respect of and offer help to these students who'd like nothing more to make her life a living hell.
If you're looking for another male student x female teacher romance, you might as well give Gokusen a go. While it sticks to comedy most of the time, the romance isn't half bad and the characters are much better than the ones from Onegai Teacher.
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Seiji gets his wish, but not in the way he thought or wanted; one morning he wakes up to find that his right hand has been replaced by a small girl!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.
Situations are thrown at the boys in both Onegai Teacher and Midori Days either by a girl alien or by a girl stuck on your hand! These boys have to make it through with funny problems and comical situations that they find themselves in.
Onegai Teacher takes on a supernatural, unrealistic approach whereas Rec could potentially happen to someone however the main characters in each have to find a new beginning and keep their relationship a secret. They are also each filled with awkward moments and sexual tension between the two main characters
Those two series are not exactly similar, but they do share a few themes. The main one would be a romance between an older alien girl and a highschool boy, the less important would be a ridiculous illness which the guy has. Qualitywise Onegai Teacher beats Tubame Syndrome 10:1, but even Onegai Teacher isn't a top of the line manga. Anyway if you read one and found the themes I mentioned earlier interesting you might want to check the other series (just keep in mind that Onegai Teacher is considerably better).