The Reuben sando is the American deli classic as it appears at Japanese specialty shops: pastrami, sauerkraut, and Swiss cheese, executed with the precision that defines this kind of kitchen in Japan. The reference is the full New York deli build, including the grilled rye and Russian or Thousand Island dressing that usually come with it. Japanese versions tend toward fidelity, treating the Reuben as a specific thing with non-negotiable parts rather than a loose template, which means the shops that bother with it have generally thought hard about cured meat, fermented cabbage, and the grill, and brought a careful hand to all three.
The craft is in the layering and the heat. The pastrami should be sliced thin and warmed so it is tender and yielding; the sauerkraut has to be well drained, because wet kraut is what turns a Reuben to mush, and many shops squeeze it hard before it goes in. Swiss cheese sits against the meat so it melts into it, the dressing is applied with restraint so it binds without flooding, and the whole thing is built on rye and griddled under weight until the bread is crisp and deeply browned and the interior is hot all the way through. The structural challenge is keeping the rye crisp against a warm, moist, fermented filling for the few minutes between the press and the plate. A good Reuben sando is hot, tangy, and cohesive, the rye holding firm against the soft inside. A poor one is soggy from underdrained kraut or too much dressing, or dull when the pastrami was thin on flavor and the cheese never properly melted.
The category bends in predictable places. The pastrami standard has a close cousin in the corned-beef build, and a turkey version, the Rachel, swaps the meat and trades sauerkraut for coleslaw. Some Japanese kitchens dial back the dressing or the kraut's intensity for local palates, while others commit fully to the deli original. The broader phenomenon of American sandwiches naturalized at Japanese specialty shops, the Philly cheesesteak and the New Orleans po'boy among them, is a large enough subject that it deserves its own article rather than being crowded in here.