The 7-Eleven tamago sando is the convenience-store egg sandwich held to a house standard. The form is the standard Japanese tamago sando, an egg salad filling between two slices of crustless soft white bread, but the konbini context is the whole story. This is the version mass-produced to a fixed recipe and a specifically formulated mayonnaise and egg ratio, pulled chilled off a shelf at any hour, and consistent enough across thousands of stores that people treat it as a benchmark. The egg salad and the shokupan still need each other the way any egg sando does, the bread cool and yielding, the filling rich and creamy, but here the achievement is that the balance is engineered to land the same way every single time.
The craft, such as it is, lives in the formula and the handling. The filling leans on a tangy, umami-forward Japanese mayonnaise blended with chopped egg, the proportions tuned so it is creamy and well seasoned without weeping into the bread. The shokupan is soft, fine-crumbed, and crustless, cut to a neat rectangle, with the egg salad spread fully to the edges so there is no dry corner and the cross section looks even. Kept properly chilled, it holds its texture for the length of its shelf life. A good one tastes clean, savory, and balanced straight from the cold case. A bad one, usually a sign it has sat too long or been stored warm, goes pasty, the bread tacky and the filling flat, which is exactly the failure the standardized formula exists to prevent.
The wider category includes the tamago salad style described here and the grilled, custard-like rolled-omelet tamago sando found at specialist shops, a different texture and a different ambition. The premium travel and omiyage versions found in airports push the same idea upmarket with richer bread and filling. Each of those deserves its own article rather than being crowded in here.