"The Necklace of Death…!!" (死の首飾り…!!, Shi no Kubikazari…!!) is chapter 160 of the original Naruto manga.
To defend Tsunade's harsh words, Shizune tells Naruto about why she is now so pessimistic and why her necklace is so important. When Tsunade was younger she gave the necklace to her younger brother, Nawaki, in the hopes it would help him achieve his dream of becoming Hokage. He died the next day, a casualty of the Second Shinobi World War, returning the necklace to her. After that she began advocating adding medical-nin to squads to prevent more deaths like her brother's. This gained Dan's attention who, also wanting to be Hokage, wished to save as many lives as possible. Tsunade gave him her necklace when they began dating to help him in his goal. He too died during the war, and in her failed attempts to save him she developed a fear of blood. The necklace came to be regarded as cursed and Tsunade lost faith in dreams and the Hokage. Deciding to prove her wrong, Naruto resumes his Rasengan training so that he can win the necklace from Tsunade.