A description of the forms of energy used in the YuYu Hakusho universe.
Spirit Energy (霊気, Reiki, or Aura in the Viz Manga) is the energy possessed by all humans. It is very powerful if used correctly, and can be wielded by any spiritually aware human. However, the strength of the energy varies between persons. It is unique from person to person, much in the same way as fingerprints and voice-prints. Energy can be converted into weapons, used to enhance the strength of the body, and heal. In the English dub, Spirit Energy was initially used as a general term for energy, including Demon Energy; this is a mistake as it is atypical for a demon to possess Spirit Energy, though this is later corrected in the later episodes during the Chapter Black Saga.
Its explained by Genkai (as the Masked Fighter) in episode 33, Spirit Energy is linked to emotions and that it is essential for one to know their feeling to control their strength. However, evidence is seen much earlier in the series as shown during Yusuke's and Kuwabara's attack on Gonzo Tarukane's stronghold when Kuwabara was angry for Yukina being tortured. This is also shown during Yusuke's final fight with Younger Toguro in the Dark Tournament when Toguro seemingly killed Kuwabara in order to bring out Yusuke's full power.
Spirit Energy is usually blue in color, but there have been some exceptions:
- Kuwabara's Spirit Energy is yellow.
- Shinobu Sensui's Spirit Energy is purple.
- M1 is yellow
- M2 is invisible, but blue when revealed
- M3 is invisible, but red when revealed
Life Energy is a last resort for demons and humans who are out of options; it kills them if the entirety of it is used. It was used when Yusuke defeated Suzaku and at the end of the Four Saint Beasts Arc. Yusuke was on the verge of death when Kuwabara transferred some of his own Life Energy into him so Yusuke could live; they both survived, though Kurama and Hiei had to carry Yusuke and Kuwabara home on their backs. It was almost used by Kuwabara in his fight with Risho. He prepared to sacrifice himself, ending the match in a draw and winning the round for his team, but Yukina shouted his name at the last second, allowing him to get his spirit energy back and win the match with his life intact. Kurama was forced to use it in order to kill Karasu, and was only spared from death thanks to the latent effects of the potion given to him by Suzuki to restore him to his Yoko Kurama form. Younger Toguro used his life energy to block Yusuke's Spirit Gun Mega, which led to his death. Hiei is the only one of the four who has not resorted to using life energy in a fight.
Demon Energy (妖気, Yōki) or Demonic Aura in the Viz Manga is harnessed only by demons. Its strength varies greatly on the user. As stated by Younger Toguro, Demon Energy is not always as strong as Spirit Energy, but it gives a pleasurable sensation. It is also often more potent than Spirit Energy, due to demons usually possessing far greater amounts of energy than humans. In the earlier episodes of the English dub this was mistakenly identified as Spirit Energy as well (particularly during the Spirit Detective and Dark Tournament sagas), though even the Japanese version accidentally refers to it as Reiki once or twice.
Like Spirit Energy, Demon Energy can be powered by intense emotions. This was shown when Hiei and Kurama ascended from B class to A class when Yusuke was killed by Shinobu Sensui. Of course, this is a rare case as demons are not known for displaying any form of compassion or friendship.
Though this is rarely used due to the confrontational nature of demons, demons can harness this energy to heal themselves. Though Rinku and Suzaku are the only ones who show it, the fact that Kurama tells Gama to use his remaining energy to heal himself rather than to continue binding Kurama proves that any demon is capable of healing themselves, only they rarely use it as demons tend to prefer using the energy for offense.
The humans who gained powers via the Demon World Tunnel seem to use this type of energy as their powers were demonic in origin, as proven by Sniper's bullets, which have traces of demonic energy in them. It is unknown if Demon energy can metamorph into a more potent form of energy, since Sacred Energy is the result of spirit energy going through a metamorphosis.
The color of demon energy varies with its user, but the anime seems to make the default color red; demon energy in the manga is not shown to be aesthetically different
- Yomi's was once shown to be purple, but is changed to green.
- Raizen's is green.
- Mukuro's is pinkish-red.
- Yusuke's (as a Mazoku hybrid) is red.
- Kurama's is purple while in the form of Shuichi Minamino, and white while in the form of Yoko.
- Hiei's is reminiscent of a flame; orange, yellow, and bits of red, but it can also be black, with a white aura, when he begins to prime his Dragon of the Darkness Flame technique.
- Rinku's is orange.
- Toya's is aquamarine; more visible when he is using the shards of winter attack.
- Jin's is either invisible and one with the wind, or blue, in the video games he appears in.
- Shura's is yellow and orange.
- Karasu's is sickly-green.
- Bui's is red, as seen when he materializes his giant axe. However, when he covers himself in his Battle Aura, his energy turns green.
- Hokushin's is pinkish-red.
- Natsume's is purple.
- Kujou's is yellow.
- Younger Toguro's is purple with bits of blue mixed in.
- Gama's is red.
- Risho's is orange.
Sacred Energy (聖光気,Seikōki) or Holy Aura in the Viz Manga is a power very few can attain. It is supposedly the most holy and powerful of all energy, the evolution of Spirit Energy.
Koenma refers to Sacred Energy the "Ultimate Aura", the highest echelon of power that not even Genkai, who mastered the Spirit Wave could achieve. Sensui, as Shinobu, awakened this energy during his ten years seclusion, which is the result of his innate talent different from the rest (even all his seven personalities). Shinobu pointed out that even if Yusuke had energy several times greater than his own, he wouldn't be able to awaken Sacred Energy.
Since Shinobu is the only one among his seven personalities that can use Seikoki, it implies awakening Seikoki requires a certain mental state of balance since all of Shinobu's alternate personalities would otherwise have access to the physical powers of his body.
It was also stated that as Shinobu, Sensui becomes "complete" because everything he was lacking before is gone. In the anime, Itsuki states as Shinobu, Shinobu's calmness and anger, as well as all other polarizing aspects of personality come together.
According to Sensui, those who used this energy were what started the belief in angels.
Sensui's Sacred Energy had a golden-yellow hue to it.
In the anime, Yusuke Urameshi appears to have manifested a type of power, that looks very similar to Sacred Energy, by mixing both his Spirit Energy and Demon Energy together. In the English dub, Koenma says that this is not Sacred Energy, this energy fusion is something new altogether. The original Japanese version gives an impression of this being Yusuke's own Sacred Energy.
- In some translations, it was said that Genkai has Sacred Energy, however, she doesn't have it.