Senta

is a loan shark from the Akagi gang.

Background
He was sent with his brother, Bunzō to collect money that Tsunade owes to their boss. To blackmail her, they steal the First Hokage's Necklace.

Search for Tsunade arc
They believed that it still belonged to Tsunade. However, it really belonged to Naruto Uzumaki, who fought them to get the necklace back. Afterward, they explain their position; either they get the money back or they have to keep trying to get it back without getting to go home and see their families. Naruto then agreed to help collect on Tsunade's debt. Ironically, they later find out Tsunade had paid the brothers' boss back his money when she and Shizune had visited their village ten years before.