Basically the story proceeds in double pairs of Mother x son, Daughter x Dad. Where they participate in a series of games where the prizes are big stacks of cash. Soon enough, and much as expected things escalate very quickly, especially the sexual innuendo.
The challenge also involves a part where the double pair has to ejaculate in a maximum span of 5 seconds. And things surely get awkward too but fueled by greed these people are willing to do almost anything.
The first scene has Miina Wakatsuki (Mother). And Aya Miura. The second scene has Shiori Amami (Mother). And Shiori Mochida.