At first, Tanjiro and Zenitsu had a rocky relationship. Tanjiro was annoyed by Zenitsu's cowardly behavior and Zenitsu was intimidated by Tanjiro's strength and determination. Despite this, they were both members of the Demon Slayer Corps and worked together during missions. Over time, they started to understand each other more, and their relationship gradually strengthened. They began to rely on each other in battle and support each other during difficult times. Eventually, they developed a strong bond of friendship and trust, and their friendship blossomed into a deep romantic relationship. They started to care for each other deeply and became each other's emotional and moral support. Zenitsu started to become more courageous and Tanjiro more compassionate. Now, they are truly in love and are devoted to their relationship.