Ushimitsu Dokidoki Koshotentan

Komiya is a struggling grad student trying to make ends meet. He meets Youzou Nishi, owner of the Nishi Bookstore, while searching for an affordable room and board, which the latter had advertised in exchange for looking after the bookstore occasionally. After living a month with Youzou, Komiya is smitten. But Youzou is a great mystery. Apart from managing a bookstore, he also has another job that Komiya doesn't know much about, except that Youzou's clients all seem otherworldly. Komiya doesn't think about it much until an earthquake and rejuvenation water turns Youzou into a child. As it turns out, Youzou also runs a pawn shop of holy miracles for gods.

(Source: Fantasista Inc.)