Aiwa Nami no Inu

At the end of the world, I asked God to "make me a dog." I wanted to be a dog and stare straight into Nami's eyes. And so I turned into one. A dog. From that day on, a neet hikikomori became the much beloved dog of Nami.
(Source: Bunkasha, translated)
Note: chapter count includes two side stories and one extra from the kanzenban edition.