If you're looking for manga similar to Shishunki no Iron Maiden, you might like these titles. All recommendations are made by Anime-Planet users like you!
In both manga main male and female characters share a secret and the secret is (possibly) embarrassaing something related to the female lead. The boy helps her out in her trouble (and it leads to a crush on her or maybe he had it from the start), but it's equally (if not more) embarrassing to him. As to the secret itself, in Sweet Poolside the girl has large amounts of body hair in various places, but Shishunki no Iron Maiden she gets a period... a freaking Witchblade period, which involves transforming into a Witchblade (don't ask). Due to similar setup, if you liked one, you might actually like the other one too.