Eudia is not the usual succubus who goes around and sucks out all semen she can get from a guy. You could describe her more like a girl that has housewife potential with good cooking and keeping your home clean skills.
Shin and his girlfriend really like their sex life, but they have one big issue. This couple is way too much scared to have a baby so they act kind of overcautious. After discussing the problem with a friend Shin agrees to try anal intercourse.