Handpainted postcard from Taro Oguchi mailed from Imazu on June 28, 1917.

During the rowing trip, Oguchi wrote a postcard to a friend back at the school dorm in Kyoto. One side of the card has his watercolor painting of Omatsu with pine trees on the sandy beach and a boat pier. Oguchi was quite good at painting.

Oguchi sent the postcard from Imazu on June 28, 1917, in the evening sometime between 9 pm and midnight after arriving from Omatsu. He sent it to a friend named Hiroshi Kodama back at the school dorm in Kyoto. However, the friend never received the postcard since he was back in his hometown in Niigata Prefecture for the summer.

The postcard was returned to Oguchi who kept it. If his friend had received the postcard, he would have certainly thrown it away (as he later mentioned in an interview). This postcard has survived miraculously and it is key evidence for the exact date when they were in Imazu where the song was created.

On the postcard, Oguchi writes about how easy it was to row to Omatsu the day before, thanks to a strong tailwind. He notes that Omatsu was a lonely place with only one lodge. They tied up the boat in the pond and rolled around on the sand till late night while gazing at the moon and dreaming of a beautiful girl. That morning, they played tug of war (it was fun). He also mentions that they were to lodge in Imazu that night.