When I first visited Hiroshima City I could not find any manhole covers with interesting designs, but in the past year or so 2 new ones have appeared. This first one shows senbazuru, " a thousand origami cranes".
Origami cranes are not unique to Hiroshima, they are a traditional item, but Hiroshima is associated with them especially outside of japan because of the story of Sadako Sasaki. Aged 2 when the bomb exploded over Hiroshima she later contracted leukemia and set about making 1,000 cranes before she died. people from all over the world now send senbazuru to Hiroshima.
The second design features the local baseball team the Hiroshima Carp, possibly related to the construction of a new stadium. I have zero interest in baseball so have no idea if the team is any good.