Mayo Chiki!, Ookami Shoujo to Kuro Ouji Recommendations
Both of these shows revolve around the interesting relationship between the main characters. In Mayo Chiki, the main character stumbles across a secret and gets tied up into the schemes of his sadistic classmate (though that is only the bare bones spoiler free plot summary). On the other hand, Ookami Shoujo also has the sadistic type character in a commanding position over a girl who shares a harmful secret (for her) with him.
-Both are about relationships born from shared secrets
-Both have the sadistic type character
-Both share at least some element of romance
-Both maintain a comedic and light atmosphere