Life☆Switch(2003)

Life☆Switch

Will was an infamous, powerful bandit leader until an old woman’s curse turned him into a small, fluffy dog. In an instant, Will lost all his influence, money, and comrades--except one. His bodyguard Sefa stayed behind. Now the two travel the world, searching for a way to remove the curse. At least, that's what Sefa would like the boss to believe. Sefa is just enjoying the ride and he won't let anything threaten his place at the boss's side.

(Source: the manga habit blog)