First of all how do they look. They look weird. They look like they've been made by an annoying fussy child who hates crusts and will only eat white bread. They're kind of tiny and contain fillings such as apple mush with cream cheese, red bean paste and chicken katsu, which just look like big chicken nuggets shoved in a sandwich.
Not really sold? Well neither was I. My Japan travel companion formed a habit for choosing terrible snacks, however it wasn't until she forced me to try her weird looking ham and cheese sandwich from a 7/11 convenience store that I discovered their unique appeal.
Like many things in Japan, why these strange baby sandwiches work is a mystery, but they do. The bread is ridiculously soft and sweet, the mayonnaise is ridiculously creamy and sweet and the ham, made of god knows what, adds nothing more than a kind of artificial but still somehow addictive hammy...ness. Still doesn't sound good? No it doesn't and I still don't understand why it was! But it wasn't a fluke either. After this I couldn't stop eating them, instead of a delicate beautifully presented bento box or a platter of sushi I'd buy a weird multi pack of Japanese sandwiches, I honestly don't know what was in half of them. My favourite became the aforementioned chicken katsu (nugget-esque) sandwich. Thick crispy batter, soft white bread and creamy mayo, it just worked! But this isn't right, I'm a food (well, sandwich at least) connoisseur for Christ sake!
One possible reason for their mysterious allure is the mayonnaise, of which the Japanese are surprisingly proud, in particular the Kewpie brand. Unlike the anemic bland Hellmanns mayo that we've all been brainwashed into believing is not only the only option but is actually tasty, Japanese Mayo is incredibly rich and buttery and pretty much makes everything as tasty and moreish as crack flavoured Pringles. But in all honesty I can't explain it. Just go there and eat them and enjoy their strange guilty enchantment.
Or maybe it's just down to those super advanced Japanese sandwich robots that definitely exist.