Sana Mizuhara lost her husband at an early age and has raised her two sons on her own. Her older brother Koichi is quiet and her younger brother Yuji is a spoiled Sana Mizuhara. Though they have completely opposite personalities, they are both healthy sons that Sana is proud of. However, Yuji is still breastfed and has little sexual knowledge. When she gives handjobs and blow jobs to Yuji in an attempt to educate him, Koichi finds out and demands his body. Before long, the brothers start fighting over Sana, but to avoid this becoming a source of conflict, Sana suggests the forbidden mother-son threesome.