Hideko Takamine's poor farming family boards a mare for the winter. Their payment will be the foal it is carrying. Her father falls ill, her mother is a judgmental and autocratic shrew, and her brothers are of no help, so it is up to Miss Takamine to take care of the mare. When the colt is born, Miss Takamine falls in love with it.
This movie is famous for being Kurosawa's first as a director.... sort of. He co-wrote the script with Kajirô Yamamoto, was credited as Assistant Director, and directed much of it, as Yamamoto was busy with another project. Looking at it, it looks more like Yamamoto's work. Thats hardly surprising. Two thirds of Kurosawa's movie as an assistant director were under Yamamoto, and while Kurosawa's themes would change, he would carry on the habit of well-written characters that show here, even in the smaller roles.
There are some fine outdoor scenes, both in the snow and the glory of a cherry-blossom spring, but the emphasis is always on Miss Takamine, who is a stubborn character, searching for something to love.
It's hard to comment meaningfully on this moment; both the star and the AD loom too large in their later work, and this obscures any attempt to define it, both in itself, as a well-written, directed, and acted drama, and in the bodies of their works; they would change and become more definite later. It's best, then, to enjoy it for what it is: a pleasant and sentimental story about a girl and her horse.