Read manga: Daisuki Na Kaiinu Ga Tensei Shite Kita

manga
Summary:

My pet dog (best friend) is now a 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 everyday with Leo who, little by little, heals him.