Yuuki grew up in a middle-class Tokyo family, living with his parents and older sister, Mirai. Unlike Mirai, who resents their parents for being distant, Yuuki maintains a cheerful and understanding attitude, appreciating the time he gets to spend with his family. He adores robots and technology, which is why he is excited to attend the robot exhibition in Odaiba, an event that sets the story in motion.

On the day of the earthquake, Yuuki convinces Mirai to take him to the robot exhibition, unaware that their ordinary outing will turn into a fight for survival. After the 8.0 magnitude earthquake devastates Tokyo, Yuuki remains Mirai’s only family companion, guiding her through fear and uncertainty with his calm and optimistic nature. His presence profoundly impacts Mirai’s growth, as she learns to embrace responsibility and appreciate their sibling bond.

Yuuki is a small, average-built eight-year-old boy with short brown hair and expressive brown eyes. His childlike innocence and gentle demeanor are reflected in his soft facial expressions, often showing joy and curiosity.

He typically wears a light green T-shirt and beige shorts, a simple and comfortable outfit that highlights his carefree personality before the earthquake. As the story progresses, his clothes become dirtied and worn, mirroring the physical and emotional hardships he endures.

Yuuki is cheerful, optimistic, and incredibly kind-hearted, embodying a sense of innocence and warmth even in the face of disaster. Unlike his older sister Mirai, who is easily frustrated and resentful, Yuuki approaches every situation with patience and understanding, acting as a source of emotional support for those around him. His unwavering positivity makes him a guiding light throughout their journey, reminding Mirai and others to keep moving forward despite the hardships they face.

Though he is only eight years old, Yuuki displays a remarkable level of maturity and selflessness, often prioritizing the well-being of others before himself. He encourages Mirai when she feels hopeless, showing a natural instinct to comfort and reassure those around him. His genuine kindness and strong sense of responsibility make him a deeply beloved character, proving that true strength is not always measured by physical ability but by the ability to inspire hope in others.

• The Catalyst for Mirai’s Growth
  Yuuki serves as the driving force behind Mirai’s character development, helping her grow from a resentful and impatient sibling into a compassionate and strong individual. His kindness and unwavering optimism remind Mirai that family is something to be cherished, pushing her to step up and protect him throughout their journey.

• Surviving the Disaster Together
  As the earthquake leaves them stranded in the devastated city, Yuuki and Mirai embark on a dangerous journey home, guided by Mari Kusakabe, a compassionate woman who helps them navigate the chaos. Throughout their journey, Yuuki maintains a brave face, comforting Mirai whenever she begins to lose hope.

• The Heartbreaking Revelation
  Yuuki’s presence is so strong and uplifting that when the heartbreaking twist is revealed his quiet suffering and eventual fate it leaves a lasting emotional impact not only on Mirai but also on the audience. His unwavering spirit remains a guiding force for Mirai even after his absence, allowing her to find strength in his memory and move forward with hope.