Hmmm in my understanding, it's usually just manga adapted from English romance novels. If you notice, some of these manga have English names of authors beside the mangaka. Once you get the hang of the way of how the titles are styled, you can pretty much predict if it's a Harlequin or not. I'm making these titles up but like "The Tycoon's Virgin Mistress", "The Greek Billionaire's Lover", "The Sheikh's Secret Baby" etc
https://www.harlequin.com/shop/brand/harlequin-romance.html

Among the harlequin manga I read, this one is actually not that bad.