This is the everyday cold sandwich, the soft-bread workhorse of the convenience store and the bakery. Tuna bound with mayonnaise, thin ham, a slice of cheese, cucumber, potato or macaroni salad, shrimp, mixed vegetables: a simple cool filling spread evenly between crustless shokupan. The defining fact is reliability, an inexpensive, consistent, well-balanced bite rather than a showpiece.
The craft is the bind and the bread. The salad fillings are bound with just enough rich mayonnaise to hold without weeping, seasoned so they are not bland, and spread to the edges so every bite is even. The bread is soft and fresh, crust trimmed, and the sandwich is cut into halves or triangles that show a clean, full face. The whole skill is doing something plain to a high, repeatable standard.
The variations are the filling: tuna and its corn and egg pairings, ham and ham-and-cheese, cucumber, crab and shrimp, potato and macaroni salad, the vegetable and mixed packs. Each is one cold filling on soft bread, and each deserves its own article rather than being crowded in here.