Synopsis:
Toujou Renya was kidnapped by a certain goddess then she gave him 2 choices. To go back to his own world, die in the next 3 days, and then reincarnated as a dog in his next life. Or try to become a god by training through a seemingly endless time. He choose the latter choice, train hard, and when he did achieve the power of the war god, he says:

"Let's go to a different world, use this cheat like power, and create a harem there!"

(Translated directly from the source page)