Isekai ja Slow Life wa Mama Naranai: Seijuu no Shujin wa Shimasodachi

Ren Natsume, who grew up on an island, loses his life after being swallowed by stormy waves while trying to save a child from the rough sea. After death, he meets the god who governs reincarnation and learns that he was never meant to be born on Earth in the first place. Instead, he is reincarnated as Lyle in the other world where he was originally supposed to be born. Loved by his new family, Lyle spends his days in peace—until, around the time he turns three, he is reunited with Amon, the beloved dog from his past life! It turns out that Amon crossed the barrier between worlds in pursuit of Lyle, eventually arriving in this land and becoming a Holy Beast. Lyle wants nothing more than to enjoy a laid-back life in another world with his beloved dog and his family, but one incident after another keeps dragging him in, making the road to a true slow life far harder than expected...?! A wonderfully gentle otherworldly fantasy begins—with a boy and his beloved dog at its heart!

(Source: AlphaPolis)