A gluten-free sando is a context entry rather than a recipe, and worth being honest about: it is any Japanese sandwich rebuilt on bread that contains no wheat gluten, usually a rice-flour loaf or a blend of alternative grains and starches. The fillings can be anything the rest of the catalog offers, from katsu to egg salad to fruit and cream. What defines the entry is the constraint on the bread, and the way that single change ripples through everything else.
The craft is almost entirely a bread problem. Gluten is what gives ordinary shokupan its stretch, its airy chew, and its tolerance of moisture, and a gluten-free loaf has none of that scaffolding to lean on. Japanese rice-bread baking has gotten good at the substitute: rice flour, sometimes with tapioca or potato starch and a binder such as psyllium or xanthan, produces a loaf with a tender, slightly dense, faintly sweet crumb that holds together better than older gluten-free breads did. But it behaves differently in a sandwich. It is less elastic, so it tears rather than folds; it stales faster, so freshness is less negotiable; and it absorbs moisture more readily, so a wet filling will turn it to mush quickly. The skill, then, is in adapting the build to the bread: slicing a touch thicker for structure, toasting the inner face to firm it against sauce, choosing drier or better-drained fillings, and assembling close to serving rather than ahead. A well-made gluten-free sando holds its shape, tastes clean and lightly of rice, and gives a coeliac eater the same handheld pleasure as anyone else. A careless one falls apart, goes gummy, or tastes of nothing but binder.
Eaten, the good versions are closer to the wheat original than the bread's reputation suggests. The crumb is a little denser and the chew is shorter, the rice flavor is mild and faintly sweet, and a filling with enough character carries the sandwich without anyone missing the gluten. It is a format defined by who it is for, and the measure of it is whether the constraint disappears into a sandwich that simply works.
The category branches by both bread and purpose. A rice-flour-only build is the most neutral and the most fragile; a mixed-grain loaf with millet or buckwheat brings more flavor and structure; a toasted hot-sandwich version uses heat to compensate for the crumb; and a dessert build pairs the rice loaf with cream and fruit. Each of those shifts the balance enough that it deserves its own article rather than being crowded in here.