Dan was Shizune's uncle and the younger sibling of one of her parents. He became passionate about medical reform after his younger sister died, pushing hard for medical ninja to be assigned to every squad. That shared vision actually brought him and Tsunade together—they started dating because they believed in the same thing.
During their relationship, Dan opened up to Tsunade about his ambition to become Hokage. He saw the role as a way to protect Konoha's villagers more effectively. It was a noble dream, but it never came to pass. During the Second Great Shinobi World War, he suffered fatal injuries that Tsunade couldn't treat, no matter how hard she tried. He died from his wounds, which had a profound impact on her.
Content compiled by AnimeList.moe from publicly available sources.
