After her daughter's marriage, the family began living together in a dual-household setup. On the surface, everyone got along well, enjoying what seemed like a happy, harmonious life. However, unsatisfied with her marriage, Rena secretly sought ways to fulfill her desires. One night, her son-in-law Satoru secretly caught her pleasuring herself. When confronted, Satoru confessed that his huge cock was so large that his wife had started rejecting him. Entranced by his thick, rock-hard member, Rena proposed to help relieve his sexual frustration under the pretense of supporting her daughter's marriage. Though initially shocked, Satoru gradually found himself drawn to his stepmother's seductive, alluring charm, sparking a forbidden new relationship.