I am not coming from the Japanese lineage of learning Reiki.
I arrived at the experience of the energy of Reiki from a different path.
I will share my understanding so that you can understand more the mechanics of how Reiki helps you when you are studying Reiki. Feel free to explore this answer, which brings an alternative interpretation based on direct experience with the essence of Reiki, answering your question .
We all are pure life force energy underneath our experience. This energy enters the human system from a location called the Spiritual Heart, which is most directly felt in the center of the chest region, slightly to the right. This energy has been called the Divine Love energy in some cultures.
Experiencing Divine Love most effectively brings the mind into peace. In order to experience this energy we put our attention to it. And since it is most easily felt in the center of the chest region, we can put our attention on this region with the intention to experience this energy, and simply stay aware, open. In this state, we will start to feel this energy, by and by we will become more aware of it.
Focusing on this Divine Love energy most effectively brings the mind into peace. And when the mind can come into peace, emotions and the body will also follow.
You can practice focusing on this energy . The more you practice, the more you will learn how to concentrate on it better. One more thing that is important is to stay aware of what is happening within you while you are concentrating. In this way, you will be able to witness the changes in yourself while you are focusing on the Divine Love energy, consciously learning in the process. By witnessing the transformation that happens while experiencing Divine Love as the awareness, you are actually coming into your experience as your true self, and this results in the evolution of your mind’s understanding, towards more Love, more Peace, more Intelligence.
So, basically, you will be most directly, consciously focusing on the source of the Reiki practice, the Divine Love energy, and since our creative energy flows (by the mechanics of life) into what we are actually focusing on, you will be most quickly creating more and more Divine Love as your experience. Since the mind seeks Divine Love as a built in mechanism, when it is experienced, the mind comes to peace most quickly. With a peaceful mind, we can be relaxed in our body also, at will. While learning to focus on this Divine Love energy, your concentration may waver into other energies within you, already occupying your subconscious mind. The learning process is recognizing that this happens and more fully focusing on the Divine Love energy, thereby creating more Divine Love, the purest energy of life in our experience, leading to the greatest possible peace, happiness, creativity, intelligence. This is not an approach of fighting, rather, the focus is to have a greater and greater awareness of the purest energy of life, but the tendency of the mind to fight may arise due to past conditioning. We continue our practice, and we keep evolving towards deeper and deeper realization, learning how our mind works and has been working in the process.
So, yes, I think Reiki can help you with relaxation, because Reiki as a discipline seems to train students to focus on this energy and to do this with the intention for self improvement. (to do it consciously, as in focusing in Divine Love and staying in Awareness). The Higher Self Teachings path I am coming from most directly focuses on these aspects of Divine Love, Awareness, so I can notice them in the explanations written about Reiki in resources about Reiki. Basically, when we really, sincerely keep focusing on experiencing the deepest truths of life, they come into our experience from whatever path we are coming from. When our awareness of these aspects increase, we become in tune with the universal intelligence of life naturally.
Reiki.org’s explanation of the word Reiki:
The word Reiki is made of two Japanese words – Rei which means “God’s Wisdom or the Higher Power” and Ki which is “life force energy”. So Reiki is actually “spiritually guided life force energy.”