Masayuki Miyamoto is the older brother of the protagonist Dai Miyamoto in Blue Giant. After finishing high school, Masayuki found employment immediately in order to help his father, who was raising three children on his own. He chose to live separately from the family, a decision driven by his desire to support them while also pursuing his own independence. Masayuki is a responsible and selfless individual who puts his family's needs before his own. His most significant action in the story is buying a tenor saxophone for his younger brother Dai, knowing that Dai had started working part‑time to save up for one. Masayuki purchased the instrument with a loan and gave it to Dai as a gift. This gesture becomes the catalyst for Dai's journey into jazz music. In the narrative, Masayuki plays a supporting role as a quiet but essential pillar of the Miyamoto household. His relationship with Dai is marked by trust and encouragement; he does not discourage Dai’s dream even though their family faces financial constraints. Although Masayuki’s personal development is not extensively explored, his choices demonstrate a mature sense of duty and a willingness to sacrifice for the people he loves. He has no special abilities connected to music or performance; his contribution is emotional and material rather than artistic.