Yanagi-ya Hozen is a long-established confectionery store that was opened over 400 years ago.
There is a receipt given to the Ozu family when they bought sweets in 1916.

Yasujiro wrote in his diary in 1918, “...I went to Yanagi-ya with my brother and ordered three boxes of Oinotomo, said good-bye to him and went to the park...” At that time he often wrote about sweets.

Perhaps Oinotomo was one of his favorite sweets.