For those who are willing to take adventure and want to travel a lot in short, there is a choice. Of course this could be hectic, but is worth taking. What you need to do is sleep on bus during night and travel during day. This will minimize your hotel cost and maximize time utilization. For those willing to travel Hiroshima from Tokyo, the round trip bus are available around 10000 yen (http://willerexpress.com/en/) . These buses depart in late evening and arrive early morning. So, if you depart in evening from Tokyo, you will arrive Hiroshima early morning. You can keep your luggage on locker at station and travel freely. I would recommend first visit Hiroshima Memorial and quickly visit to Miyazima island. Then come back to Hiroshima for evening travel and take bus back to Tokyo which will arrive early morning. There are lots of restaurant all the way and you better taste Hiroshima Okonomiyaki, really good.