They are called onigiri <3 i made my own ones and they are SO tasty!
the white base is rice, the black stripe is not for decoration, its vor holding them withoud getting dirty fingers ... the black stripe is nori (seaweed) on the top of the onigiris is furikake (vegetable taste)
the onigiris have a filling. the filling is a mix from egg, mayonnaise, sandwich bred and cheese
You eat them with soy sauce