Japanese commerce seems to have found a rather big market into treating loneliness. From the existence of Host Clubs, bars where the menu is not only food, but a good conversation with one's designated “host” as well, to cafés where the waiter plays a role of one's doting younger sister. Of course, it is probably also indicated by the infamously declining birth rate.
Rent-a-Girlfriend is a bizarre thing to read, if one not understand it's target audience. It's a new dimension to The 40 Year Old Virgin, with the exception that the protagonist is supposed to be relatable to the audience — he's unbelievably socially awkward and not in a way that derives humor from it, but is meant to invoke a sense of relatability and it essentially seems to exist as a way to vicariously cope with loneliness, as is surprisingly common in Japanese fiction.