Daisuki na Kaiinu ga Tensei Shite Kita

My pet dog (best friend) is now an elementary student!? Corporate slave salaryman Tomoki meets a boy named Leo. Suddenly the boy claims that he was Tomoki's pet dog in his past life and that this time it's his turn to protect Tomoki. A story about life every day with Leo who, little by little, heals him. (Source: Frontier Works, translated)