One day, Keitaro unexpectedly transferred to a different world where he met Nia, a half-demon girl, who urged him to "make a child" with her. The two of them went traveling in search of gateways to different worlds when Rosette, another half-demon girl, appeared... The girls of a different world fight over the valuable "human male" using their sex appeal. ♡

Note:
The Japanese title is a play on words. The Kanji for 'lifestyle' is 生活 (seikatsu) but the author replaced 生 (sei) with 性 (sei), which becomes 性活 (seikatsu), or 'sexual activity.' Since they're pronounced identically in Japanese it gives it a double entendre, but this can't be translated in a way that retains that.