The said vessel helps their Dungeon Capturer capture a Dungeon and forms a Household Vessel from that candidates Djinn, or if the assistant makes a strong connection with the Dungeon Capturer. When a Household Member first uses their Dungeon Capture's power, a Familiar of the Djinn shows up and grants it to them. It seems that if the King Candidate does not have his/her Metal Vessel, the Assistant can not use their Household Vessel at all.
The activation of a Household Vessel actually has two stages, the normal stage and the more powerful stage called Assimilation (同化, Dōka).
Assimilation is the fusion of one's self with the Household spirit of the Djinn inside the Metal Vessel. By doing this, the user becomes more powerful but at the cost of becoming less human, proportionally to the number of times this technique is used. There is a possibility that in the end, not only the body, but the consciousness will assimilate with the Djinn as well, and the user's heart will vanish. This is why the user says, "I consecrate my body to you". Forcing the process can be lethal.
A household vessel is basically the same as a Metal Vessel. They are made of metal objects that have deep meaning to the user. It can be weapons, accessories, jewelry, etc. A small magic circle appears when the Household Vessel is activated.
- Main Article: Household Members