"Mifune vs. Hanzō, the Conclusion!!" (ミフネVS半蔵、決着!!, Mifune Bāsasu Hanzō, Ketchaku!!) is chapter 532 of the original Naruto manga.
Mifune reminds Hanzō of what Hanzō had told him during their prior fight as Mifune lay there dying from the poison he received from Hanzō's kusarigama strike. As Mifune laid there dying, Hanzō appreciated his bravery and gave him an antidote for the poison. Reminded of his prior life and in a tremendous demonstration of will, Hanzō places his faith in Mifune and overcoming the talisman that governs him, he commits "seppuku" (切腹, Literally meaning: stomach-cutting) with his broken kusarigama. Piercing the internal venom gland located within his body in the process, an enormous poisonous cloud is released that paralyses the entirety of Hanzō's movements, creating an opening for the Fifth Division to exploit in order to seal him away for the remainder of the war.