Yomi is first mentioned in the manga as Ragnarok's main rival and was later revealed to be a group led by the disciples of the members of Yami's One Shadow, Nine Fists and serve as the supporting antagonists of the series following Ragnarok's defeat. They are considered the rivals of the Shinpaku Alliance and their main goal is to not only defeat and kill Kenichi Shirahama, the disciple of Ryozanpaku, as a way to prove that they are the strongest, but to also show that the Satsujinken is the true way of Martial Arts.
Like their Masters, they each have incredible fighting skills and a large number of resources at their disposal, such as Boris Ivanov's military commandos and large sums of money, and have the same symbols as their respective masters. These symbols are engraved on golden emblems given to each member. Each is different in shape and appearance depending on its owner, and are used to not only represent Yomi membership but also as a means to officially issue a challenge, should a member encounter an opponent they deem worthy enough to fight to the death with. A Yomi challenge is apparently initiated by the member handing his/her symbol to the fighter they wish to battle. From that point onward, the symbol would remain in the hands of the one challenged until they are defeated or killed in combat by the one who issued the challenge; only then can the symbol be retrieved. Should the member be defeated instead, the symbol then becomes property of the victor, possibly as a means of giving them the option as to whether or not they would want to replace the defeated member in the Yomi ranks after that. It is also the victor's decision of what they do with the emblem. In Kenichi's case, the 4 emblems he owns (Boris Ivanov, Sho Kano, Ethan Stanley, and Radin Tidat Jihan), have remained with him as mementos of his battles. The emblems are also noted to be quite valuable as the members of Ryozanpaku tend to stare at them greedily considering how much they could pawn each emblem for.
Each member also has a nickname based off mythical beings, though Boris's, Kajima's, and Chikage's has not been revealed. Unlike their masters, they have no name for their group that signifies their rank among their peers since they are comprised mostly of just the disciples of the One Shadow, Nine Fists group (Yami has a much larger group base that happens to have ranks).
Out of the ten strongest members orginially introduced, seven (including Chou Enshin) have been rendered inactive: Shō died after fighting Kenichi, Boris was defeated and left in order to find his master, Ethan is currently in India with his master after losing to Kenichi, Chou was defeated and replaced by Tanimoto, and presumed to be dead, and Rachel is currently following orders from Isshinsai Ogata since her master was defeated. She is also looking for her master as Ivanov is. Tirawit Kōkin was defeated by Kenichi at Okinawa base and possibly returned to Thailand with his master, and Jihan was defeated and was presumed to have died after his fight with Kenichi but survived and returned to his country after Jenazad's death. Rimi Kokorone and Ryuto Asamiya left Yomi after having been been enraged and used by Ogata for his experiments, leaving five active members, including one Kenichi has yet to meet.
Over the course of the Yami/Yomi saga, more members of Yomi have been introduced to replace the main members who have been incapacitated. Isshinsai Ogata has been revealed to have more than one disciple, which Ryuto was thought to be the only one. Akira Hongo has also taken up more than one disciple to replace the one he lost on Despair Island (Sho Kano).
Each member of Yomi have studied under one of the members of One Shadow Nine Fists, has an emblem that has its symbol. It is an emblem of defiance that is delivered once your opponent agree to fight, or when they fought. Apparently this made of pure gold. It has not yet been seen if the executing Sheet Yomi Hachio possess these.
As a sub-division of Yami, have great economic capital, which have facilities for training or leisure time. It has been shown that several, and usually meet there when their teachers are deciding something, or when they are called.
Yomi means "yellow flow", in China,it is the road to hell. This name follow the saying of Katsujinken :"Joining Yomi is walking on way to darkness.".
Tirawit Kōkin was the only member Kenichi defeated in the YOMI saga to not give him his symbol.