My Junior was My Mom in Her Past LifeMy Junior Was My Mom in Her Past Life; Zense ga Hahaoya Datta Kouhai; 前世が母親だった後輩

A mother who, in her past life, passed away when her child was only two years old. She reincarnated with memory of past life retained, and became a junior of her child - now 18 years old - in his high school.