Woof Woof Story: I Told You to Turn Me Into a Pampered Pooch, Not Fenrir!, Vol. 1 (light novel) — Inumajin

Due to extreme fatigue and terrible work conditions, Routa dies without having done much with his life. As he breathes his last, the only thought in his mind is to be reborn as the dog of a rich family so he can enjoy the good life. A merciful goddess takes his plight to heart and grants his final wish, sending Routa to be reincarnated as the pet of a wealthy young lady! It seems like he got exactly what he wanted, but it soon becomes clear that he's much too large, much too powerful, and gets in too much trouble to be any regular old dog!