Betray in the Box

Young Jijii's Rookie Shonen Jump entry.

This is the story of the Betrayal Box... A young swordsman named Io Shinmen, who is striving to master the most powerful swordsmanship, Tengen-ryu, encounters Gepannu, a beautiful phantom thief being pursued by the Yagyu Kengekitai, a national police force. Through this encounter, Io realizes that his mission is to seal the box.