Both are entertaining battle parodies - one of the historical warlord era and one of the modern-day host clubs. But really, you're watching because they have large casts of beautiful guys looking super-cool. And it's worth it.
Both series focus on a Prince-like, or at least incredibly wealth male lead character. In both series, the more aristocratic elements are usually played off for laughs and are 'popcorn' type of entertainment.
Both dramas feature rich boys and one poor girl who attends school on a scholarship. Both are over the top comedies with the main hero being a "prince" character and the heroine being blunt and not interested in him at first.