If you're looking for manga similar to Osamake: Romcom Where The Childhood Friend Won't Lose, you might like these titles.
As an overweight child, Makabe Masamune was mercilessly teased and bullied by one particular girl, Adagaki Aki. Determined to one day exact his revenge upon her, Makabe begins a rigorous regimen of self-improvement and personal transformation. Years later, Masamune re-emerges as a new man. Handsome, popular, with perfect grades and good at sports, Masamune-kun transfers to Aki's school, and is unrecognizable to her. Now, Masamune-kun is ready to confront the girl who bullied him so many years ago and humiliate her at last. But will revenge be as sweet as he thought?
I like romantic comedies. However, romance doesn't develop like that in reality. There was once a time where I thought that. Encountering a girl who fell from the sky, my school life changes with a clang.
Yuuki Narito's new seatmate Yui Takatsuki is the notorious “Seatmate Killer,” who strings guys along before breaking their hearts. But Yuuki's so clueless he might be immune to her charms! And so begins a fierce competition between two seatmates in this hilarious rom-com.
Ryoko Masaki is a serious class president, yet she has decided to become a delinquent to catch the attention of her childhood friend, Masato Todoroki. The reason is that as a discipline committee president, Masato always goes out of his way to remind delinquents of their attires, yet he doesn't pay any mind to the serious Ryoko. That's why Ryoko decided to dye her hair and shorten her skirt, and when Masato saw her, he was devasted and concerned. Is this what Ryoko had hoped for...?
Kurumi lives under one roof with her father and her overprotective brother, Ataka. One day, she reunites with Nagio, her childhood friend. Now a young man, Nagio doesn’t hesitate making advances—much to Kurumi’s dismay—kissing her out of nowhere and telling her how he has always liked her, in the process totally wrapping her around his finger. And while Kurumi is put off at first, she eventually finds herself head-over-heels for Nagio…
Follows a boy named Jun who is childhood friends with two twin girls with different personalities. He ends up in a love triangle with Rumi, who looks boyish but is an maiden on the inside, and her twin sister Naori, who is a cute otaku.
I, Ruka Yamamoto, suffered from a strange disease that caused me to become ugly and so I was looked down upon and bullied at school, at my part-time job, and even by my unkind relatives. However, when I returned from the USA after undergoing a treatment, I found that I had become a ridiculously handsome man (as I should have been)! Moreover, because I used to be obese, my muscles strengthened and I became an all-arounder no matter what I did. I became the best in sports, the strongest in fights, also I became more fluent in English than my teachers, a very high-spec individual. Now that I’m back, my youth’s revenge begins…!
In a rural junior high school, a boy and a girl pledge eternal friendship, and two years pass without any progress in their relationship as they become destined for one dream...! Inuzuka Himari, a cheerful girl who has yet to find her first love, and Natsume Yu, a passive boy who loves flowers, are still best friends in their own gardening club in their second year of high school. "If Yu can't get married, I'll have to take responsibility for you." "After Himari said that, I'm having a hard time because your brother started calling me, 'My brother-in-law!'" However, when Yu reunites with his first love from the past, the wheels of their relationship suddenly go haywire! Will Himari, who has discovered love, be able to break free from her "ideal friend"?