Every year on the Sunday closest to the 15th there is an archery competition at Sanjusangendo- the temple of 1000 Kannon on Nana-jo south of Kiyomizu. This dates to the 1600's when the competition was to shoot the entire length of the temple. Nowadays you only have to hit a target half the length, still a difficult task from what I saw. Anyway, the event is from 9-3:30 and there are thousands of contestants who give it a try. The contestants are usually people who became 20 this last year and thus who celebrated coming-of-age on Seijin no hi. They appeared to be members of archery clubs from colleges across Japan. It was worth it just to see the kimono they had on (the same one's they wore for their coming of age ceremony earlier in the week I am sure), but the archery made it especially cool. Part way through they switched to a few rounds with really good archers and smaller targets. They still had difficulty, but hit the targets much more often than the 20 year olds before them. We only stayed for about an hour, but were glad to have seen it. It was crowded, but we were able to find a place to watch a little of it on the stands about midway across the field.
Also, FYI the entrance fee to the temple is free on this day and they have several stands for Tai-yaki, okonomiyaki, tako-yaki, sweets and so on for hungry kids.