Even though Hiroshima and Miyajima are a long day trip from Japan it is one worth doing. A day to these places shows amazing history, culture and scenery which is nearly unrivilled in Japan. With a bit of planning and organisation a day trip here is more then doable.
You will need to start your day early with a JR Rail Pass. The cost of Osaka to Hiroshima is about $108 AUD without the pass. We caught a 7:18 train from Shin Osaka station which arrived in hiroshima at around 9.05. If possible reserve a seat on the Shinkasen a day or two before.The train is an easy ride and you can order food on board.