The tanto swords are the smallest, generally no more than 50cm/19.6inch. It is a kind of sword which is single-edged and short-edged. Sometimes these can just be called “Japanese”. We manually grind the edges, so they can through tatami mats, made from bamboo.
Of course, the most convenient are usually mineral water / purified water bottles. These can be used multiple times and they are cheap. The most important thing to remember is to dry the surface of the water bottle to prevent the blade from rusting.