Buying a round trip ticket, using only one way

I am an American currently living in Japan. My job will be ending in a couple months and I will be flying back to America, staying there for a couple months, then receiving a free flight back to Japan. I need to buy a plane ticket to return home, but I only need to go the one direction.

One way tickets tend to be more expensive than round trip tickets, so my idea is to buy a round trip, fly to the U.S., then give the airline some excuse about why I won't be able to use the return flight home.

Are there any possible negative ramifications of doing this? Anecdotes welcome.

If a round trip indeed costs less than a single one way ticket, just buy that and not use the return flight ticket. There is no need to explain to the airline why you are not using the return ticket. I have spoken to Delta Airline about the very issue when a friend of mine was flying home to LA last fall and a representative told me while they preferred (naturally) we buy a one way ticket for a one way trip, there wasn't any penalty/fine for simply not using the return ticket.