Many people know the Reiki hand positions on the upper body from their first Reiki level: the solar plexus, the chest, the belly. For self-treatment in particular, a sequence like that is a good thing to hold on to. I lay my hands on myself every morning right after waking up, for example. In the Shingon tradition, though, the upper body has a background that most people don't know, and that's what this article is about. Two terms are central here, kaji 加持 and the five elements.

Kaji, adding and holding 加持
Kūkai (774–835), the founder of Japanese Shingon, explains this term in his treatise on awakening in this very body (Sokushin jōbutsu gi) with an image. The sun of the Buddha is reflected in the water of the human heart, and that is ka, adding. That the water of the heart can take in and hold the sunlight is ji, holding. In other words, it takes both, the power that comes and the person who receives it.
I find this image very helpful for understanding Reiki, too. When you lay your hands on someone, you are not "doing" something to them. The force comes, and the receiver takes it in and holds it in their own way. For the Shingon tradition the central source of this light is the Great Sun Buddha Dainichi Nyorai, whose light is present in everything. In the Diamond Realm Mandala his Siddham seed syllable (Siddham is called Bonji in Japanese) is vaṃ वं, and in the Womb Realm Mandala it is a.
The five elements in the body 五大
Shingon speaks of five great elements (jap.: godai 五大): earth, water, fire, wind and space. You can see them in the five-ring pagodas (jap.: gorintō) at Japanese graves, where a cube for earth, a sphere for water, a triangle for fire, a half-sphere for wind and a jewel for space are stacked on top of each other. Put simply, it is the human body in the form of a pagoda.
In the traditional order, earth belongs to the lower body, water to the area around the navel, fire to the chest and the heart, and wind and space to the head. So when you work with Reiki on the upper body, you are touching the area of water and fire in particular, and the transition to wind at the throat. You'll find the seed syllables of the five elements in the article on chakras and Reiki.
The areas of the upper body 六位
In many Reiki traditions there are hand positions for these areas of the upper body. Each of them has its own character, and in Japanese culture several of them have a meaning of their own.
Collarbones and throat
The collarbones mark the threshold between the trunk and the head, between what we feel and what we say. In the Indian chakra model the throat chakra sits here. Many people notice tension in this area as a feeling of tightness.
Breastbone and heart
The area of the breastbone is where people feel joy and grief. In Japanese the word kokoro 心 means heart and mind at the same time, and in esoteric Buddhism the heart is the place where the moon disc is contemplated in meditation.
Ribs and breath
The ribs protect the organs and give the breath its space. Many people notice their own breathing here, and how it becomes deeper during a session.
Solar plexus
The upper belly is often experienced as a place of inner warmth. Many practitioners describe a pulsing sensation here.
Lower belly, hara and tanden
The hara 腹 is the center of gravity of Japanese practice, from martial arts to calligraphy. About two finger-widths below the navel and further inward lies the tanden 丹田, the "elixir field". Many people describe this place as a kind of coming home.
Pelvis
The pelvis is the foundation of the trunk, and in the Indian model the root chakra is connected with it. In the five-ring pagoda this is the cube at the very bottom that carries everything else.

More than a sequence 地火風
If you look at the upper body in this way, the hand positions are no longer just points you work through one after the other. They become a small landscape of elements, from the earth of the pelvis to the fire of the heart. With hibiki and byōsen, the perception through the hands, you can sense where your hands are actually needed, and sometimes that is somewhere quite different from where you would expect.
In Shingon Reiki the hand positions are connected with the beings of light, seed syllables and mantras of the Shingon tradition, which goes back to Kūkai in the 9th century. How that works in practice is something you experience in the live events and in the community.

Which area of your upper body do you feel most clearly when you lay your hands on yourself?
Discover the way of Kaji
In Shingon Reiki the hand positions are connected with the Shingon tradition. If you like, take a look at which starting point fits you.
Your path into Shingon Reiki Chakras and Reiki