
These patterns were a source of endless fun for samurai.
Towards the end of the Heian period, the Emperor and his gamer friends were too busy playing mono-awase (“thing contest,” see this post if you need a refresher) to pay much attention to the rest of the country.
Meanwhile, out in the real world where crime needed fighting and order needed keeping, local lords hired tough guys with swords to act as police or military, leading to the rise of the warrior class: the samurai.
The samurai almost immediately began copying some of the habits of their social superiors, including the games they played. But between stabbing bandits and shooting Akira Kurosawa films, samurai had far less patience for faffing about chasing songbirds and giving excessive opinions on the color of autumn leaves.
Mono-awase changed, from forms in which things had to be grown, found, crafted, or improvised on the spot, into less demanding games.
Incense-awase turned into jishu-kō (“ten types of incense”): ten chips of incense were mixed up and lit and players tried to identify them by smell alone. (They called it “listening” instead of “smelling.” I guess smell was much too coarse a sense for such a subtle and elevated activity as sniffing magic smoke.)
Incense was hugely popular, and enormous effort was put into finding and developing new kinds. Like wine snobs today, they would say things like “ah, yes, I sense hints of apricot, musk, and jealousy,” while normal people rolled their eyes.
Several even fancier versions of jishu-kō were invented. In kumi-kō, the incense was chosen to match themes from classic waka poetry, legends, or the seasons. In the most popular variant, Genji-kō, the incense was supposed to be remini...scent of episodes in The Tale of Genji. You have no idea how popular Genji was. It was like if you added the popularity of Harry Potter, Marvel, and Game of Thrones together, then multiplied that by the disappointment of Game of Thrones’ last season. Everyone was Genji-mad.

In Genji-kō, five carefully selected sticks of incense were cut into five pieces each. Then five of those 25 pieces were randomly selected. Players listened to these chosen five, and had to decide which, if any, matched.
They would mark their answers using five vertical lines (for the five sticks of incense) connected by horizontal lines (for matching sticks), creating pretty little geometric patterns. The astute student has already noted that there are 52 possible combinations, including all matching and all different. (Actually, if you have noted this, you should consider a degree in mathematics with a specialty in combinatorics.)
Each combination stood for a different chapter in Genji (which has 54 chapters, but the first and last received no love, or at least no geometric incense picture). The connection between these patterns and the chapters in Genji was about as strong as that between your astrological sign and your future: in other words, there was no connection at all, but people were all about it.
Each game ended with a set of Genji symbols that people didn’t do much with besides taking them home and pondering over their meaning. Edo period Tinder profiles were probably filled with Genji-kō symbols.
These patterns of vertical and horizontal stripes became super famous and were used to decorate fabrics, pottery, and lacquerware. You can still buy kimonos today with a genji-kō pattern.
Wonder if they did that with kiseru too