Tanjiron is the one of the quest NPCs that you will meet and accept quests from. He is located on the bottom of the rocks where the Sword Styles unlocker is located in Dimension 1. Tanjiron can only be interacted with when you have equipped the Water Style Sword Style, and has a current total of 5 quests. Rewards of Tanjiron's quests include Yen and Chikara Shards, and the ability to master the Water Style Sword Style to the Sun Style Sword Style.
This page contains all brief explanations about the current quests given by the quest giver Tanjiron.