The Dai-Ichi Doku (which means "Foremost Poison") is a clan of the organized crime world collectively called the Yakuza. Notable members of the Dai-Ichi Doku include:
- Eiji Hasegawa: Eiji was Oyabun (essentially the leader) of the Dai-Ichi Doku when Manhunter (Mark Shaw) was being hunted by Dumas I. Because he owed a debt to Mark's father, Eliot Shaw for honorable actions taken by him shortly after World War II, Eiji had the Dai-Ichi Doku intervene to safely transport Mark out of Japan. He was eventually killed by Dumas II.
- Kazuo Hasegawa: Kazuo was the son of Eiji and was involved in a few of Mark Shaw's adventures. When his father was killed by Dumas II, Kazuo sought revenge. He wore Mark Shaw's Manhunter costume and fought Dumas II only to die at his hand, but his sacrifice enabled Mark to save his family and ultimately avenge the deaths of both Kazou and his father.
- Ryu: Ryu helped Mark Shaw rescue his family from Dumas II and ultimately became Oyabun after the death of Kazuo. While Oyabun he was instrumental in bringing a large cache of automatic weapons (refered to as 'the Dragon's Hoard' into Japan - which brought him and the clan into conflict with Mark Shaw and the Suicide Squad.
- Itto Senzaki: Itto was a Lieutenant of Eiji Hasekawa.
Equipment: None known.
Transportation: None known.
Weapons: None known.
- No special notes.
- No trivia.