No, Tanjiro does not obtain Rengoku's sword in the "Demon Slayer: Kimetsu no Yaiba" series. The sword that Tanjiro wields throughout the story is his own sword, which he received from his family. Tanjiro's sword is a black Nichirin Blade, and he uses his own unique breath style, known as the Water Breathing technique, in combination with his swordsmanship skills. The sword holds sentimental value to Tanjiro as a connection to his family and his journey as a Demon Slayer. While Tanjiro greatly respects Rengoku, the Flame Hashira, and considers him a role model, he does not inherit or use Rengoku's sword.