Why does the Koto (Sou no Koto) have 13 strings? The reason for this is anecdotally preserved in China.

It is said that the koto (Sou-no-Koto:13-string zither commonly known in Japan today) originated in China.
In fact, it is said that there is an interesting anecdote about the koto(Sou-no-Koto) in China.
I would like to introduce this anecdote to you this time.

In China during the Qin Dynasty, there was a master of a 25-stringed instrument similar to the koto(sou-no-koto) called the Shitsu.
The master musician, who had two daughters, divided the Shitsu into two parts, one with 12 strings and the other with 13 strings, so that the sisters would not fight over the Shitsu when it was handed down to the governor of the family.
Later, the 12-stringed Shitsu became the Korean peninsula a 12-stringed instrument called “kayagumu,”, and the 13-stringed Shitsu became the Japanese koto(sou-no-koto).

What do you think?
The authenticity of this story is not certain, so please take it as a legend, but it is an interesting anecdote.

Incidentally, there is a theory that there used to be a 50-string shitsu.
The pedal harp has 47 strings, so if it did exist, it would have been a rather large instrument.