This oyster festival on Miyajima island is held each year in February during oyster season. It celebrates one of Hiroshima's biggest exports—you guessed it—oysters! The event is held right next to the ferry port and a no-brainer if you are into seafood. You can get many variations of oysters: grilled, fried, in soup, battered and fried in tempura ... They also sell other seafood like eel (anago 穴子) and other fish.
If you don't want to stand in line for a long time, plan to get there very early, even before the main festival starts. During the festival you can enjoy traditional Japanese cultural performances.
Traditional plays with flute and taiko drum music playing while the actors dance and fight in colorful costumes on the main stage. In combination with the festival, you can enjoy the famous Miyajima island sights.
Fun Fact: In Japanese, the word for oysters, kaki, shares the same spelling as another food—persimmons. So how can you tell them apart? They have slightly different inflections, but here's a great mnemonic to help remember: kaki (fruit) has a rising inflection (think picking persimmons from a tree), whilst kaki (seafood) has a falling inflection (think reaching down into the sea).