In a distant past of Japan, a lazy and selfish Taro Junya Kato loves to eat and sleep and wrestle with the animals. With no direction in his life, a Tengu appears that grants him a special potion that changes everything. With this potion, he gains the strength of a hundred men—but he can only use it when he is helping others. After drinking the potion, day by day, he begins to understand what it means to help others, first by fighting Akaoni Kazuo Kumakura to save Aya Mina Tominaga, a young girl gifted with the flute, then by helping others in his village collect fire wood.
One night, his grandmother tells him of his mother’s transformation into a dragon. This revelation sets Taro on a journey to find his mother, a mission that tests his resolve and his growing sense of responsibility. Before he begins the search, Taro again confronts Akaoni after hearing from the animals that Aya was captured by Kurooni Kazuo Kitamura. After a brief but fierce fight, Akaoni agrees to help Taro save Aya from Kurooni, and in the end, Taro discovers that his actions have also freed a village from the terror of the two Oni, the latter forced into the former’s service.
Taro’s adventures do not stop there. He helps Akaoni by sending him skyward to serve the thunder god, and the village celebrates his deeds. Yet the journey continues as he encounters a troublesome old woman in a rice paddies plot. A successful harvest year follows, but the storyteller’s truth is revealed only after a conversation with a giant serpent living in the lake beside the old woman’s fields. The serpent’s counsel leads Taro to share the fruits of his labor with the old woman’s former employees and others, leaving her with little and teaching him about fairness and generosity.
From the serpent’s word, Taro learns that nine mountains away lives a Yamanba who can point him in the right direction. He seeks out the legendary figure and, in a tense exchange, the Yamanba reveals clues about his quest and hints at her own role in the serpent’s fate. After a narrow escape from the Yamanba, Taro is overwhelmed by a chilling encounter with the icy threat of the yukionna.
The next morning, Aya finds Taro nearly frozen but alive, a miracle she helps to sustain. With her aid, he reaches the lake where his mother Tatsu Sayuri Yoshinaga now lives. Tatsu explains why she was transformed: as a mother heavy with child fulfilling her duties to her unborn child, she needed to eat, but her actions left nothing for the rest of the village, prompting her dragon-like change.
Taro proposes a plan to improve life for the villagers back home: build a new settlement with expansive rice paddies that can sustain everyone. The two of them set out to break the dam that holds the lake, and their efforts succeed, but at a great cost. Tatsu’s body is broken, and as the lake drains away, Taro fears the worst. Yet, in a turn that brings both sorrow and relief, his mother’s life is returned and she becomes human once more. The triumph is not just personal; the new flooded lowlands bring prosperity to many, helping not only Taro’s village but many others along the way. Through endurance, sacrifice, and a growing sense of responsibility, Taro reshapes his future—and the future of the people who depend on the land.
