If you've ever sat in a goma ritual in a Japanese temple, you'll remember it. The priest feeds wooden sticks into the fire, the drum beats, and the mantras get faster and more intense. The smoke rises to the ceiling, and the heat hits your face. For many people this is one of the most impressive rituals in Japan.
Goma 護摩 is one of the central rituals of Shingon, and also of Tendai and Shugendō. It's anything but a quiet prayer by candlelight. Fire, heat, smoke and sound take hold of all the senses, and that's exactly why the transformation it stands for starts in the body.

The word goma ゴマ
Strictly speaking, though, these two characters were chosen mainly for their sound. Goma is a phonetic rendering of the Sanskrit word homa, the Vedic fire offering, from the root hu, "to offer." So the meanings of the individual characters are a nice bonus, but the word itself points back to India.
From India via China to Japan 火
The roots of goma go back to the fire offerings of Vedic India. There, offerings were given into the sacred fire to renew the connection between human beings and the cosmic order. When esoteric Buddhism developed in India, it took up this fire ritual and gave it a Buddhist meaning. The fire kept burning, but what was offered changed. Now it was also one's own attachments and the passions that cloud the mind.

From India the practice reached China, and from there Kūkai 空海 brought it to Japan in 806, when he returned from Tang China. His master Huiguo had given him the full transmission of the esoteric teachings, and the goma was part of it. In Japan the fire ritual then became one of the central practices of Shingon, on Kōyasan and in temples all over the country.
Fudō Myōō and the fire 不動明王
A goma can be dedicated to different Buddhas and protective beings, but the most common is the goma for Fudō Myōō 不動明王, the Immovable Wisdom King. He's understood as a wrathful manifestation of the Great Sun Buddha Dainichi Nyorai 大日如来, and his task is to cut through obstacles.
Fudō holds a sword in his right hand that cuts through ignorance, and in his left a rope with which he binds the passions. He sits on a rock surrounded by flames, and in the goma, the fire of the ritual is understood as his fire. His wrathful face is the wrath of compassion, a bit like a parent protecting a child from danger. There's a saying in Shingon that Fudō Myōō is the other face of the smiling Dainichi Nyorai. Where the cosmic Buddha appears in stillness and light, Fudō appears in fire and resolve.

How a goma takes place 法
A goma follows a precise order, and every step has a meaning. The priest sits in front of a square fire altar surrounded by ritual implements. The fire is ritually purified before it's lit, so that it becomes the "mouth" of the being the goma is dedicated to. Fudō's mantra is recited again and again during the ritual. Into the fire go gomagi 護摩木, narrow wooden sticks on which visitors have written their wishes and prayers. In many temples you can write a stick yourself before the ritual. According to tradition, the wishes rise with the smoke, transformed by the fire.
Shingon also speaks of an outer and an inner goma. The outer goma is the visible fire on the altar. The inner goma takes place in the practitioner's heart, where the fire of wisdom burns up the passions.
Five kinds of goma 五種
Not every goma is the same. Shingon distinguishes five kinds of ritual (goshuhō 五種法), each for a different purpose:
Sokusai-hō 息災法, for averting misfortune and restoring peace. The fire altar is round and associated with the color white.
Zōyaku-hō 増益法, for increase, of prosperity, merit and beneficial forces. The altar is square and associated with yellow.
Chōbuku-hō 調伏法, for subduing obstacles, meaning the forces that cause suffering and not people. The altar is triangular and associated with black.
Keiai-hō 敬愛法, for love and harmonious relationships. The altar is lotus-shaped and associated with red.
Kōchō-hō 鉤召法, for summoning, that is, calling in what is needed.
These details aren't pedantry. As in a mandala, every element stands in its place because it reflects a cosmic order.
Goma and Reiki 靈氣
What does a fire ritual have to do with Reiki? At first glance not much. Reiki is quiet and gentle, goma is loud and hot. Yet they share one principle, which is transformation. Blockages and attachments are loosened so that what lies beneath them can become free.
In a Reiki treatment this happens silently, through presence and the hands. In the goma it happens through fire. In other words, in the goma you see with your eyes what happens invisibly in a Reiki treatment. Both have their roots in the same world of esoteric Buddhism, Shugendō, Shintō and shamanic Daoism that Usui drew on. In Shingon Reiki I keep this context in view, so Reiki isn't seen as a wellness method, but as part of a living tradition in which fire ritual, mandala, mantra and the laying on of hands belong together.
A goma can't really be described, it has to be experienced. If you travel to Japan, many temples hold goma rituals regularly, often daily, and visitors are usually welcome to attend. Have you ever written a wish on a gomagi?