The Amida Tong were a group of assassins featured in the James Clavell novel Shōgun as well as the mini-series based on the novel. According to the novel and TV series by the early 1600s they were the deadliest assassins in all of Japan.
Members of the Amida Tong trained all of their lives to be the perfect assassin. Their operatives were masters of infiltration, able to sneak into fortified and secured installations to murder their targets. Such members were trained to end their own lives if facing capture or failure of their mission.
An Amida Tong assassin was sent to assassinate John Blackthrone. The assassin was able to penetrate Lord Toranaga's castle and was able to dispatch a guard patrolling the hallways. He almost made it to Blackthorne's room but at that moment the Lady Ochiba stepped out of a room and realized he was in the hallway. She ran off, sounding the alarm. The sleeping Blackthorne was awakened by the commotion and was able to dodge the assassin when he came in and attempted to cut him open with his sword.
Blackthorne was able to kick the sword out of the assassin's hand and push him away. The assassin took out a small knife he had been carrying and started considering how to attack Blackthorne. At that moment three samurai burst into the room and placed themselves between Blackthorne and the assassin. Seeing as how his mission had failed and he had no chance of surviving a fight with the three armed samurai the assassin turned his knife on himself, ending his life.
Toranaga and General Hiro-matsu arrived. Hiro-matsu quickly uncovered the assassin and discovered the mark of the Amita Tong tattooed on the assassin's chest.
Suspiscion quickly fell on Lord Kasigi Yabu as he was one of the few men who had contacts in the Amida Tong. Toranaga summoned Yabu to meet him the following morning to watch the sunrise. Yabu got the message that Torananga was not happy about what had happened last night.
Ultimately it was uncertain who hired the Amida Tong to kill Blackthorne. Yabu had the contacts to arrange for an Amida Tong assassin to kill Blackthorne. The Jesuits working the islands were not happy about the presence of Blackthorne and might have hired the assassin - either by using their own contacts or working with Yabu - in order to prevent Blackthorne from sabotaging plans for Japan that the Jesuits and some European nations were making or impeding trade.