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Seiji gets his wish, but not in the way he thought or wanted; one morning he wakes up to find that his right hand has been replaced by a small girl!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.
Both manga feature a girl who turned very small for some reason and now has to (more like wants to, in case of Midori no Hibi) live with the male lead. In both series one of the main characters is a delinquent, in Midori no Hibi the delinquent is the male lead, but in Yankee Figure it's the girl. So yeah, the male leads are not very alike, the guy from Yankee Figure is more like the doll otaku guy from Midori no Hibi (maybe because he IS a doll otaku).