Michiyo Kobayashi is the younger sister of protagonist Chitose Kobayashi. She contracts typhoid fever during the narrative events and dies from the illness. Her death marks one of the early personal tragedies to impact the Kobayashi family amid wartime conditions.

Michiyo's portrayal emphasizes typical childhood behaviors, particularly her attempts to join play activities. One scene shows her asking Chitose for permission to play with a paper ball, which Chitose initially denies. After Chitose leaves the ball to pursue other games, Michiyo retrieves it and plays alone. This paper ball later transforms into a symbolic family keepsake following her death.

Her absence echoes through the narrative as a lingering presence. The family exhumes and transports her ashes during their escape from North Korea after Japan's surrender. Facing immediate danger from advancing Russian forces, they destroy all identifying documents and personal effects, including Michiyo's photograph, to hide their Japanese origins. The paper ball persists as one of their few tangible mementos of her existence throughout the journey.

No expanded media beyond this narrative provides further depictions or developments of Michiyo Kobayashi. Her character primarily functions as an emotional representation of familial loss within larger sociopolitical conflict.