The Villainess and the Demon Knight manga volume 3 features story by Nekota and art by Seikan.

Marquise Cecilia is engaged to Lord Lucas, second prince in line for the throne and wielder of the fabled magic sword Eckesachs. Despite being rough in the bedroom, he's completely devoted to her. But while Lord Lucas is busy battling dangerous magical beasts, Cecilia's ex, the former second prince Felix, arrives unannounced. He's unable to accept his treatment of Cecilia is what lost him his inheritance. He places the blame on Cecilia and attacks her! Will the protection magic around Cecilia hold out until Lucas returns? Or will she be at the mercy of Felix's violent temper?!