So it wasn't Yuuhi having ecchi physics that protected him from her. it was Yunika unintentionally causing the lucky pervert moments all along because she was attracted to him?
Lust Inducement via Pheromones: The sites of pheromone production and other secretions in a Charmian's deep dermis produce numerous psychoactive chemicals, which, when inhaled or absorbed through the skin, induce in an individual a sexual desire no matter how much of a gentlemen they are. This also works on animals. However, certain individuals (such as Gid and Rito) are capable of resisting this.