There are some ways for sushi restaurants to offer their food. You can eat a la carte, running sushi, buffet style and so on. In Delft I have discovered a new way: In rounds. Let me explain: In each round you are allowed to order up to five small things, e.g. one nigiri sushi, three maki rolls, two spring rolls, etc...You can repeat this process for two and a half hours. In case you are not able to finish the meals they are charged additional to the lump sum price you pay for this kind of "all you can eat". Here the link to Umai Sushi in Delft.