nice split of topic, indeed a good question put!
many of us would see reiki as an 'energy' modality, and many, on the other hand, will see the 'energy' aspect as manifestation of 'reiki in action' as against real substance of reiki, per se.
leaving the energy aspect of reiki experience away from the discussion for the time being, i would like to come straight to the question whether any 'spirits' are involved in reiki, or that it is one's own 'spirit' which is at work when reiki happens ? these questions are interlinked and should not be compartmentalized unless we know the things for sure, which obviously we are far from
it would be of interest if we see these questions from the often-believed viewpoint that the knowledge streamed to us through physical 5 senses is not complete... the reality exists even beyond our this knowledge... many people have had this experience of deep meditation that they come to know about other realms/worlds during some moments... when they got a 'glimpse' of something they have not seen or preceived through physical senses.... thus, definitely a world of possibilities exists beyond our knowledge.
one of such possibility is that we all have a spirit that permeates or co-exists with our physical presence... we may call it a spirit or its semi-physical exhibit can be called our aura... things are always interlinked, you see... a spirit is not marked by definite boundaries, since it is non-physical... it is marked by possibilities, small or large, present or future, near or remote... this gives us some idea that it might be possible that our individual spirits somehow interact (or can interact) with each other at some plane or in some arrangement... non-religiously speaking, it is also possible that spirits of human beings (as well as other living / non-living things) collectively compose a master–spirit in which trillions of spirits are woven like a fabric... the command over this spirit, if some believe so, would be called God, or else... but something like that....
reiki, as i would happen to believe or feel, is an interaction with spirit... a reiki experience is an outcome when this interaction takes place... reiki is not a start off event... it is the event itself... when we reiki, the interaction has already happened or has begun... reiki exists in happening, not in starting something like healing, energy experience, etc. these are manifestations of something that has happened already.... by this general description, it is well nigh impossible that we interact exclusively with our spirit... we are definitely tiggering a 'synapse' to other spirits when we are interacting with ours, since all are linked.... during this, we may feel their presence, their help (spirit or reiki guides), etc. but it might be a little too much to say that reiki invites other spirits to the chain... this may happen, but not as a prerequisite... the possibilities are endless when we interact with our spirit... this is gateway to many new experiences... some experiences we are able to couch in our understanding, some experiences are so subtle that they go without any meaningful explanation of our vocabulary or narrative...
interestingly 'ghosts', 'daemons', 'bad spirits' have got a lot of stuff attached by socio-cultural and equally religio-dogmatic context... unless we start with a state of mind that is non-flavoured, and is ready for anything to accept, as against what 'it should' accept acccording to so-called doctrines, we are far away to link that phenomenon with something called reiki that has, even when having a specific japanese origin, transcended to something 'universal' or 'global'.... there might a division like japanese reiki, or western reiki, but having said, there is no confusion about universality of reiki per se !
cheers
Salman