Oscar Joaquín de la Rosa

Oscar Joaquín de la Rosa was Yasutora Sado's grandfather. He appears to be a quite strong old man, but with a gentle character. After the death of Chad's parents, Sado moves to Mexico with Oscar Joaquín, who adopted  and raised him. Chad refers to him as "Abuelo" (Spanish for Grandfather).

During his early years, Chad was extremely violent; exploiting his advantage in size, he intimidated and hit any other children who annoyed him. Oscar Joaquín tried to teach Chad to be gentle, but was initially unsuccessful. One day, the fathers of the children Chad fought, seeking to punish him, attacked Chad. Oscar Joaquín stepped in between them, taking Chad's punishment without retaliation. Chad was inspired by this example to become a decent person. Afterwards, Oscar Joaquín gave Chad a Mexican coin. The coin was minted sometime between 1823 and 1909, and has the words "Republica Mexicana" (Mexican Republic) engraved on it, as well as the Mexican National Emblem. The monetary reform of 1905 minted Mexican coins with the words, "Estados Unidos Mexicanos’," are seen on the Mexican peso today.

Years later, when Oscar Joaquín had died, Chad made a vow that he would never fight unless it was to protect others, as instructed — even if his own life was in danger. The coin would come to symbolize this vow, which Chad now claims to hold more value than his own life.

When Abuelo died, Chad decided to return to Japan.