Shuumatsu no Harem

both takes place in the future and are harem genres  

Both are about a male lead having to use his manhood to save the world or the people he care about. 

Action, story, sex, fanservice - What more can you ask for? These shows grant them all 

Both are post-apocalyptic series where the main character uses science to try to undo the illness that caused the apocalypse in the first place. 

The possibly wildest imagination one sex could have of another. Must watch for extremists. 

they both have the same premise a pandemic causing the population of men capable of having sex to drop but in shuumatsu harem the desease actually causes death and in modaete adam kun the disease only causes impotence shuumatsu harem has action scenes 

World's End Harem is like a sci-fi version of School Days to me. Plenty of borderline Hx moments. Doi is similar to Makoto in terms of his lack of self restraint growing as the series progresses, in addition to his, well, relations with the harem members. They are both love or hate series. If you love one, you will love the other, and vice-versa.