One day, mother Saki accidentally discovers her son's phimosis and contacts her husband, who is away on business. However, her husband doesn't take the matter seriously, so Saki resolves to handle it herself. In the bath, she carefully washes her son's uncircumcised penis, explaining that proper hygiene inside and out is essential. Gently wiping away grime from under the glans with her fingertips, she uses her saliva to clean his sensitive head, responding warmly and attentively to her son's reactions. Soon, her son begins trembling with arousal, and their relationship starts evolving into something new.