When people first hear about a Reiki initiation, the question that comes up right away is what actually happens. In English it's usually called an attunement, in German an Einweihung, and in Japanese reiju. Each word puts the weight somewhere slightly different. What interests me here is where the practice comes from, because its roots go far beyond Usui, through Japan and China all the way back to India.
Kanjō, pouring water on the crown 灌頂
In ancient India, abhiṣeka was a coronation rite. The new king was washed with water from sacred rivers, and that installed him in office. Esoteric Buddhism took over this form and gave it a spiritual meaning. Put simply, the person receiving it isn't installed in a worldly office. They're connected with the power of a Buddha.
Kanjō came to Japan by way of China. Kūkai (774–835), the founder of Japanese Shingon, received it in 805 in Chang'an from his master Huiguo (Japanese: Keika). After he came home he passed it on in Japan, and it has been at the heart of the Shingon tradition ever since. There are several forms. The best known among lay people is kechien kanjō 結縁灌頂, literally "the kanjō that ties a karmic bond." Large temples such as Tōji in Kyoto and the monasteries of Mount Kōya still hold it for the public today. Denbō kanjō 伝法灌頂, on the other hand, is the transmission to someone who is meant to carry the lineage on.

Body, speech and mind 三密
To understand why Shingon considers a transmission possible at all, I'd like to explain one basic principle. Shingon speaks of the three mysteries (Japanese: sanmitsu 三密): body, speech and mind. The body expresses itself through hand gestures (Sanskrit: mudrā), speech through mantra (Japanese: shingon 真言, "true word"), and mind through inner focus on a Buddha or a Siddham character (Bonji in Japanese). In Kūkai's understanding, the body, speech and mind of a Buddha and of a human being aren't fundamentally separate. What's remarkable about this is that a person already carries everything they need for their spiritual path.
The word Kūkai uses for how these come together is kaji 加持. In his treatise on awakening in this very body (Sokushin jōbutsu gi) he explains it with an image. The sun of the Buddha is reflected in the water of the human heart, and he calls that ka 加, adding. That the water of the heart can take in and hold this sunlight he calls ji 持, holding. In other words, it takes both, the power that comes and the person who receives it. I find this image fascinating for understanding any initiation.
Reiju in Usui's tradition 靈授
In the society Usui founded in Tokyo in 1922, the initiation is called reiju. How Usui himself carried it out in detail isn't recorded in writing. Still, I think it's very likely he knew kanjō, because according to his memorial stone he studied Buddhist scriptures intensively, and because in his day large temples regularly held kanjō for lay people. It's also said that in this tradition reiju wasn't received just once but again and again at the meetings. That fits well with the idea that a connection deepens with every encounter.
For more on the sources about Usui, see the article on Usui's historical sources and the one on the memorial stone.
The symbols and where they come from 種子
Initiations are often mentioned in the same breath as the Reiki symbols, so it's worth taking a closer look. One of the Reiki symbols goes back to a Siddham seed syllable whose original form I found during my research in Kyoto. Others are made up of kanji. In Shingon, a seed syllable (Japanese: shuji 種子, literally "seed") stands for a particular Buddha or Bodhisattva. It's a kind of shorthand that holds the whole power of that being, a bit like the way a whole plant is already contained in its seed.
If you're curious about the individual characters, the background is in the articles on the Reiki symbols and the Siddham script.

The levels 段階
In Japanese the levels are called shoden 初伝 (first transmission), okuden 奥伝 (inner transmission) and shinpiden 神秘伝 (transmission of the mysterious). Each level comes with its own initiations. I see the levels less as a staircase you climb and more as layers that open up over time. Further along the path in Shingon Reiki, initiations into Buddhist protective beings, mantras and the Siddham characters are added.
How people experience an initiation 体験
Everyone experiences an initiation differently. Some describe warmth in their hands or at the crown, others see light or colors behind closed eyes, and others simply feel calm. Some notice nothing special in the moment and only realize in the days afterwards that their hands feel different. These are all personal experiences, and none of them is the "right" one. I was pretty skeptical at the start myself and wanted to experience it before believing anything.
Why an initiation needs an encounter 相承
You can read books about meditation and just start. An initiation is different, because it's about a lineage. Shingon calls this shishi sōjō 師資相承, the handing-on from master to successor: from Huiguo to Kūkai, and from Kūkai through many generations to today. That's why an initiation is always a personal moment between people.
How I give initiations myself is something I deliberately don't describe here. That belongs within the protected setting of the initiation. If you'd like, you can experience it at one of the live events, and it's possible across distance too, as I explain in the article on distance initiations.
Step into Shingon Reiki
If you'd like to receive an initiation yourself, Shingon Reiki Level 1 is the way in. It's held live online on Google Meet over two days, in English, with five initiations: four into Reiki and one into the Medicine Buddha. Next dates: see events.
Shingon Reiki Level 1 Your path in Shingon Reiki