Yokorenbo: Immoral Mother

Plot seems similar; son trys to plan his way to get sex from his female family members. 

Similarity : Both tell the story about having sex with older sister Different : Ryouichi Fujisaki is much more evil rather than Yutta. I will not tell you why because it can be said as spoiler. 

Similarity : + MC having sex with his "Mother" & "Sister" + The main story is "dissatisfaction" from MC about how his condition family after re-marriage, this also become reason why he built relationship with his "mother". Different : + Ryouichi Fujisaki victim is his own mother, Tomonori victim is "just" step-mother  

Similarity : Both anime tell the story about love between mother & her son Different : Yokorenbo MC is much more violent & dark, compared to Gibo no Toiki which much more kind 

Similarly: - key word Sex between son - mother and other female family members...!