Kono Inu to Kitara Mago no Koto shika Kangaeteinai: Kensei Maou no Yarinokoshi

The "Demonic Invasion" lasted for hundreds of years, and countless heroes were cut down by the Demon Lord during their reign…! Until the hero Terios, known as The Last Hope, finally defeated the Demon Lord and brought peace to the land. But the hero Terios vanished, and the Demon Lord, thought to be dead, is miraculously reborn… as a dog!? This is the story of the last Demon Lord, now all soft and fluffy, desperately trying to live a peaceful life while protecting his granddaughter, now a fugitive targeted by all of creation.

(Source: Kadokawa, translated)