Daisuki na Kaiinu ga Tensei shitekita

The pet dog (best friend) that he was reunited with is an elementary school student!? Tomoki Takakura, a corporate drone, has a chance encounter with a boy named Leo. Leo suddenly informs him, "I'm your reincarnated dog...!!?" "This time I will protect you." Everyday, bit by bit, Tomoki is healed by his beloved Leo. (Source: Frontier Works, translated)