A use for dried octopus is to flavor the water used to cook the rice in. This is probably pretty normal in some places.
Simmer the octopus in the water for a while, and strain it out. Add the vinegar and rice, bring to a boil stirring, then simmer for about 15 minutes. A rice cooker is probably a better idea, but I'm cooking for folks where octopus is really not normal, so they don't get through much rice. Oh, you probably want a bit of salt in the water, but not soy sauce as that turns the rice all muddy.
Probably octorice goes well with cucumber marinated a bit with some salt and white wine vinegar, or other such pickled veggies.