I feel like having an argument over this, LOL. I've seen writers just use spiritual energy (which is probably the best we're going to get), but there's also reiki and chi out there. So, which is it? I've researched it quite a bit, but am still uncertain. Here are my findings:

Ki: Commonly known as chi or qi (Chinese words for ki) and commonly referred to as 'spiritual/vital energy', ki is the basic, universal life energy which is believed to flow through all matter. Individuals who dedicate themselves to spiritual teachings and practice self-awareness meditation are believed to be able to possess higher levels and awareness of their ki.
* My assumption is that this energy is not found in yoki-manipulating yokai, or in other words, it is not found in apparitions who break free of the universal life cycle and live off of their own energy, yoki. Yokai are considered to be an imbalance to the otherwise perfect cycle of life energy, and followers of any religion may exercise the spirit of a yokai with the intention of bringing them back into the natural cycle.

Reiki - As opposed to ki, which is the art of being capable of manipulating your own energy and exerting it at your own expense (depletion), reiki is the ability to basically be near someone and 'open' yourself as a conduit, allowing another to subconsciously absorb through you what their body needs from an eternal and limitless source of healing energy. To summarize, reiki is the word you use to specify 'healing reiatsu', seeing as it is a common and specific practice of 'manipulating' energy.

Additional terms associated with ki are reiatsu and reiryoku.
Reiatsu - (spiritual pressure). Someone capable of manipulating ki (spiritual energy) is also capable of manipulating said ki into something, said 'something' being generally called reiatsu. Reiatsu can be anything from the energy put into a sutra or an ofuda to a purifying barrier (kekkai). The power of an individual's reiatsu is measured and limited by their reiryoku.

Reiryoku - The measure of total potential achieved by an individual in terms of ki and their capable manipulation of it into reiatsu.

**Reiatsu and reiryoku are tricky to differentiate (at least they were for me with the definitions I found online). The following sentence may help: Reiryoku is the term for the total potential with which someone can manipulate their ki and exert it into reiatsu.

To me, it seems that reiki is based on healing and nothing else, but I could be wrong. What are your thoughts?

Reference links:
1 - Reiki and Qi Gong
2 - "Spiritual Energy"
I actually read about reiatsu and reiryoku a few weeks ago, and now can not find the article I read but there are plenty of Bleach sites to read up on them from.

In general, I think that 'spiritual energy' is the best by default since, but what is your word preference from above?

Seeing that all forms were used in one anime or the other, I usually use reiki to picture Kagome's spiritual powers or youki for Sesshomaru's. Using reiatsu or reiryoku reminds me of either Bleach or another anime I can't seem to put my finger on and the whole idea for the story vanishes.
Reiki or spiritual energy (though the title for what Kagome can do is a bit too long, thus I often if not every time use the first explanation ) is what both the mangaka and the one that made the Inuyasha series used, so why should I make up another word for her miko powers.

Sure, anyone can use synonyms or visual effects in their stories such as tendrils of light, or ribbons of power or things like this, but I prefer the old and over-used words to state whatever I want to state I know I'm always a bit too lazy to make something up but from the words you just enlisted above I would not use chi, reiatsu or the other long word that reminds me of a dragon's power simply because I make my already fuzzy mind wonder to shows and ideas that have nothing to do with the task at hand - and that is the fics I write.

Now, shoot up another question regarding Kagome's and Kikyo's powers
Though my knowledge in the matter is a bit rusty I want to talk about this too so shoot!

Hmm, I never watched much Bleach. Sorta got to the part with the 'evil' characters who have white bone-like masks covering parts of their faces, then lost interest, so I don't have that issue with words. I still feel that the more 'complex' words honor the nature of Kagome's and Kikyo's energy, but I'm glad to know how people could be distracted from a story because of the words used. I'm also the sort who challenges facts in the series, such as Kaede's village being in the east and not in Sesshomaru's supposed domain and Edo being a thriving village five hundred years ago instead of the little thing Kaede's Village is. You can redesign the compass and say that Kaede's Village will become absorbed by the neighboring, rapidly growing Edo, but it's still annoying that such things were not covered initially.

I wouldn't be surprised if Reiki had been chosen in the actual story simply because it originated in Japan (whereas ki is merely a translation for the Chinese concept), but then again much of Sesshomaru's clothing and accessories have mainland influence, so that should not be applicable. Also, while it's called reiki in the series (I'll trust you on that, I've never actually caught the word) I've never seen anyone use it in the series for healing. More often than not it's yoki that heals, which had me commenting in an old fanfic that spiritual energy was simply glorified as righteous by its wielders but its base nature was destructive, yoki is more constructive (you can make things from it and it can grow with the energy from a spirit connected to spiritual attributes).

Thank you very much for this information Aura! I personally use reiki because thats the first one I heard of, and I like how it sounds. lol

Hmmm, I wonder.... Reading the definition you posted above on ki, Aura, I got a few ideas and questions that bug to come out.

Ki is the life energy that flows through everything (like a human, dog, amoeba, a rose, rock, water droplet, etc... all matter, as it said), right? And it is universal, as in the same for everyone?
So... can a person (if he has enough experience, or can manipulate/is highly aware of his own energy) link their own energy to another's (or another thing's)? If so, could they manipulate the other's energy? Could they borrow it? Absorb it?
--> Because, my interpretation of the definition is that it may be possible.

Would spiritual energy reflect the 'owner's' qualities like emotions? Where is ki housed? What is it linked to?(Like, does it depend on the soul? Heart? Blood?)What about the energy of the soul? Does the soul istelf have any energy or power?

Because, in Inuyasha, it's Kagome's soul that gives her the enourmous power... I think. (Individuals who dedicate themselves to spiritual teachings and practice self-awareness meditation are believed to be able to possess higher levels and awareness of their ki.)--> But, she didn't dedicate herself to spiritual teachings. How can she have more energy/power than someone(like Kaede) who has?

And, this definition strikes me as a buddhist one(or another oriental religion). What does the Shinto religion specifically have to say about this? (Because, she is by all intents and purposes a miko - shinto priestes)

~lily

Another great forum post!

I have always used reiki because, like what was said before, it was just what I was first exposed to through fanfiction.

*considers changing* Maybe in the next fic