In feudal Japan, society was ruled by the samurai class. The samurai, as a warrior caste, distinguished themselves from the rest of society by wearing two swords and a unique topknot hairstyle. The samurai topknot had several variations, and you can emulate those styles with your own hair, provided it's long enough.
Grow your hair long enough that when it's tied into a ponytail, the ponytail that measures the length of your hand from the tip of your middle finger to the base of your palm at the wrist. If you don't have naturally straight hair, straighten it first. Making a samurai topknot using of wavy or curly hair proves much more difficult.
You can create a different look for your topknot depending on how much time you want to spend making it. Three main styles were popular during Japan's Edo period: the chasen-gami, a topknot with the knot flared out to resemble a tea whisk; the mitsu-ori, a topknot with the hair well-oiled, tied in a high ponytail, folded forward over the crown then back over itself and tied into place; or the futatsu-yori, a topknot with the hair folded forward and shaped with a razor. The samurai sometimes shaved the front of their head up to the crown, leaving the sides and the back to grow. This made wearing a helmet in battle more comfortable and prevented any loose hair from falling into their eyes. However, this step was optional. If you want a quick version of the topknot, you could emulate the early Chinese-influenced version: a simple ponytail tied at the crown of the head and folded back on itself so the knot points upward.
Making the Topknot
Wash your hair and condition it, then dry it. Bend over and let your hair hang straight down so you can reach all of it. Brush your hair and remove all tangles. Gather it in a ponytail as high as possible and tie it in place using a soft elastic hair tie without a metal connector. Don't pull your hair too tight into the ponytail, which would damage to the roots. Loop the tail over two fingers and place a second hair tie over the base of the topknot. You can use hairspray to hold it in place.