I'll reframe the question. Think of the soul as an entity. Where have we seen this entity in Naruto before? There is one very specific instance where we actually see the 'soul' itself. I'd also be careful in conflating the soul with the spirit, and vice versa.
Okay - who are the Ronin in the RP, what is the nature of spirituality and the spirit, what is spiritual kenjutsu, and what is the 'soul?' What can Ronin do that a Yin Release Master cannot, and vice versa?