The second to highest class, beings possessing A class strength level are almost exclusive to demon world while the Keikai barrier is up; the only exceptions are if a human attains this strength, a demon achieves this level in human world, or the barrier is removed. Prior to the Keikai barrier's removal A class demons could not move between the worlds without aid. While exceptionally powerful and rare in the human world, they are relatively common in the demon world. However, compared to the power of an S class demon they are very weak; so weak in fact that they are used as mere foot soldiers of the Three Kings.
From the demons of this class seen in the series, A class are the traditional depiction of demons, with some being humanoid with various inhuman features such as horns, fins, eyes, etc; to very humanoid beings. From what is observed from the series, A class do not react to instinct, but instead, will use their brains and "senses" in order to judge how strong an opponent is and observe before taking action. As shown, when the first true A class demons that are shown in the series, are shown watching C class (probably more likely D class) gather in mass at the open Keikai barrier to enter the human world, commenting on the simplicity of their lesser brethren, while sensing the overwhelming powers of Sensui, Kuwabara, Hiei, and Kurama in his Yoko form, leave before they become involved in the conflict. Further evidence of their intelligence is in the buildings they have created. In Mukuro's realm, it is a spider-like structure with hellish rooms, healing chambers and altars to ancient gods. Raizen's realm is a huge tower with a separate building in which the king resides, and Yomi's realm is an advanced, futuristic realm with cloning technology, visual aids that display stats, tearooms, a throne room, corridors and large buildings. They also displayed a system of government prior to the Tournament to decide the next King of the Makai. Raizen's was a large training center for the monks that served him and for a resting quarters for himself, Mukuro's was a mafia-like militarized state that had healing chambers to restore fallen warriors, and Yomi's was similar to a monarchy, where the nobles would discuss with him, the future state of affairs, while keeping his good graces. Likely due to his ability to hear everything in the kingdom, his territory was relatively peaceful, although there were some political assassinations for certain positions. In conclusion, the A class were comparable to civilized human beings in their culture and ways of thinking. In terms of society, A class demons would compose the upper middle class and are still considered exceptional in even in the demon world. In terms of power, a single A class demon could cause immeasurable destruction in the human world and nothing short of a nuclear weapon could destroy one of them.
Kurama - Former (Yoko Kurama) Alive (Shuichi)
Hiei - Former
Yakumo - Deceased
Yomi's Assassin - Deceased
Kuronue - Implied, Deceased
Touou - Alive
Seitei - Alive
Residents of Spirit World
King Enma - Implied (Manga) and (Movie 2)
Special Defense Force - Alive
Humans that have level equivalencies with A class
Shinobu Sensui - Former, Promoted to S class, Deceased
Kazuma Kuwabara - Former, Promoted to S class(Manga)
Yusuke - Former, Promoted to S Class
Tsukihito Amanuma - Revived, connoted
Yu Kaito - Revived, connoted
Asato Kido - Connoted
- According to Sensui, A Class demons have power roughly equivalent to the gods of various religions and myths (in the dub, he states that they are on par with the Titans of Greek mythology).