Yes. Azazel is actually going to be the first, but it will be Koneko to make a huge scene of it.
Would you be willing to share that worldbuilding? I'm interested.
Both actually. It isn't a great problem if handled carefully, but most knowledge about Senjutsu is kept secret by the few that mastered it. Anyone in canon that talk about Senjutsu? Most of their knowledge is just educate guesses and preconception. For Kuroka and Koneko the ability to use Senjutsu is completely instinctual, so even them wouldn't be able to exactly tell you how and why most of what they do work.
To be clear: there isn't malice, evil, bad thoughts and all that shit mixed up with natural energy. Senjutsu chakra is completely neutral, neither white nor black.
But because of that it is easily influenced by the emotions of those who channel it. Senjutsu didn't make Kuroka crazy, but she was so angry that her control slipped and the Senjutsu chakra amplified her anger to unreal levels. Koneko's fears are always been unfounded, even if, indeed, trying to use Senjutsu while she was consumed by her fear of it would have bad consequences.
Since most shinobi receives their training during teenage-hood, the ninja scrolls were created in order to train them without first having them master their emotions. No matter how much their emotions run rampant, they wouldn't be influenced by Senjutsu chakra.
Of course, the tainted energy isn't actually purged but just expelled...
Please bear with me if I make a mistake as I summarize- I don't know how I would attach a word doc to this or if it is possible- moving on
Basically I had magic being an extra- dimentional energy, noone knows the origins (there are many theories) but it comes from elsewhere. It passes through all things on a deeper level (think quantum mechanics) and mages use it by learning to shape it as it passes through. Everyone's metaphysical pattern reacts to the ambient energy that is magic in different ways, in fact every thing reacts differently, animals plants and minerals, natural magical phenomenon occur when geology, geography and magic combine to create things like ley lines (paths of strong magic flow due) and other areas of high or low magic and even more fantastic phenomenon (think the at worlds end level of magicka) since for people this pattern includes emotional and intellectual elements It is possible to direct the flow of mana with training.
The Terms I used were capacitance for how much mana your pattern could hold at once, inward and outward voltage for how quickly mana was drawn into your pattern or expelled from your pattern. Amperage was the same but for amount of energy not how quickly (think of the relationship between the speed of the water and the diameter of the hose) There are more complex details that modified how mana was shaped but basically magic was done via mental and emotional conditioning and ritual behaviors to alter your pattern so mana has a specific effect when expelled, The many ways magic is used all revolve around the many was to do that. It is closely related to the other energies I mentioned
Ki is the energy in ones patter related to one's physical self- master martial artists achieve awareness to shape the part of their pattern related to their physical self to achieve effects, from training and conditioning that makes you faster and stronger than realistically possible, to more esoteric effects like altering one's body shape or life extention- things like dragon ball style ki blasts are when ki adepts approach magic in methods. Overall it surpasses magic in physical enhancement through permanent shaping of the body physically and metaphysically but magic is better in terms of variety and in expelled attacks- ki blasts are much less efficient then spells, because they are more flexible metaphysically and more energy efficient. Mages train to draw in more energy all the time for spells, Ki adepts train to increase their energy, but it is intended to fuel the long term enhancements their other training provides, not immedieatley expelling it as an attack so it is more training to increase how their pattern manages energy reserves- they increase their capacitance instead of their voltage. As such ki adepts tend to draw on that reserve of energy in the physical part of their pattern for effects, so ki blasts can cause physical exhaustion since it draws on that source.
Shamanism or Rei trains the mental or spiritual portion of one's patter the same way (think shaman king) their arts revolve aroud effecting things on the spiritual level, exorcisms, blessings seances, all work via channeling this spiritually attuned energy. More over shamanism works via working with spirits, either via cooperation or domination the energy is channelled through the spirit as well, achieving much more diverse effects- basically using the spirit as a mold or prism- like a mage would shape their own pattern for an effect. This branch of shamanism relies on improving the shaman's spiritual fexibility, awareness and capacity to better shape the energy as it is channeled to achieve effects such as willing possession, allowing the spirit to effect the physical world or as an aid to more complex spiritual feats. It is more energy effecient than ki adepts in external effects, in essence investing in the spirit instead of one's self, but it has the same problem in energy recovery, and is often less flexible than magic because it very much depends on what spirit is involved, Master shamans can control the manifestation via channeling to mitigate this.
Reiki (basically naruto chakra) combines the above two, and strangely enough becomes a lot like magic, training and combining spiritual and physical energy in their metaphysical pattern to achieve effects, they can enhance themselves physically, generate spiritual effects (mainly creating illusions but their are some that have shamanistic esque techniques) and combine them to expel it like a magic spell. the problem is like the above two it has endurance issues- users are limited by their reserves. Many expelled techniques are stylized or flashy- because of the spiritual element requiring a sort of dicipline and imagination that means that established methods can take years as the right training to reliably produce that mindset is developed.
On a social notes while magic is wide spread and so are ki use (eastern martial artists and western knights, basically many long lives martial traditions) and shamanism (mostly in tribal groups or religious positions or as part of certain magical traditions) reiki users are reclusive due to being shunned. Basically early in the history of it's use in the east they were subjected to a witch hunt by the estabishment- advisors of magical and spiritual matters could not percieve it as they could others- to many magic users it was if they were pulling the energy for what they saw as spell out of nowhere. combined with the variety of effects and how it fit none of the other groups the users were demonized- some litterally thinking there was a demonic source or deal related to the source of the energy they were using, other just wanting to drive away threats or competition. Most users are from reclusive communites or hermits- except for those that found patrons or allies that hid them- these became the ninjas either as independent clans or working for a noble patron they honed the stealth potential of thier esoteric art over time. In the modern day the prejudice is mostly gone, because the art is unknown, most think ninja techniques are one the other arts, and they rarely see enough to discover otherwise.
Senjutsu is when a third element is added- essentially adding magic to Reiki- it is dangerous to start adding the power of mana to the metaphysical metabolism of Reiki users, with out training and dicipline to properly filter and mix the energies- the associations in the mana absorbed can create effects such as petrification, spontaneous combustion or transformation and mutation, or more subtle internal difficulties as the mixed energies have a spontaneous effect. True sages consist of certain hermits amongst the ninja or other reiki comunities but there are people that in their life time have achieved certain limited effects, typically only one or more techniques.
in terms other crossovers in the methods there are certain traditions that have elements of the other methods. Most common are those shamans that know some magic or mages that know method for dealing with spirits, then there are ki adepts that have magic talent or study it to round out their abilities over their life time, there are many old master martial artists that know some magic, typically small spells or ones that work with their style of ki use- Reiki is the only mixed use that has a dedicated population and has its own category. Since it all ties back to ones' own pattern when one becomes skilled or expirenced enough overlap in the methods in at least in some small ways becomes inevitable.
