Why am I banned from buying a tuna knife?

My brother went to Japan recently, and I asked him to buy me a knife. As anyone who has entered the bowels of a restaurant knows, Japanese blades are highly sought after. I had to decide between an 18cm utility knife or a metre-long Maguro bōchō. The carbon steel of the latter can fillet a 500-pound tuna in a single cut. In Japan, it is wielded by two highly skilled fish butchers, and it usually comes with a wooden scabbard as protection for the blade – and anyone standing near it.

Boringly, I opted for the utility knife. I reasoned that I could always buy a razor-sharp, 24-inch blade online at a later date. However, my hopes have been dashed. This week, the government announced new legislation that classified the tuna knife as a ‘ninja sword’.