In many Japanese homes there's a household altar, the butsudan 仏壇, literally "Buddha platform." It's usually a small cabinet with doors, and inside are a Buddha image, the memorial tablets of the ancestors and a few offerings. For many families it's the place where they connect with the Buddhas and with their ancestors every day.
In this article I'll show you how you can set up a simple Buddhist altar for your own Reiki practice at home. It doesn't need to be a museum-grade reconstruction. What matters is that it supports your practice.

Why an altar? なぜ
The simplest answer is that the place where you practice shapes the practice. An altar creates a spot that's different from the rest of your home, and when you sit down in front of it, your body soon knows that practice is about to begin.
In Shingon, a place of practice is called dōjō 道場, literally "place of the Way." In the temple, the altar is where the practitioner performs the rituals in which kaji 加持 takes place, the mutual connection between the power of the Buddhas and the practice of the human being. A home altar is of course much simpler, but you can think of it as a small dōjō in this sense.
The elements 要素
You don't need much for a Buddhist altar, but what you place on it should have a meaning for you.
A figure or picture of the Buddha, bodhisattva or protective being you practice with, for example Dainichi Nyorai or Yakushi Nyorai, the Medicine Buddha.
Light stands for wisdom, which dispels the darkness of ignorance.
Incense purifies the space and marks the beginning of practice. It is one of the oldest offerings in Buddhism.
Fresh flowers stand for beauty and, since they wilt, also for impermanence.
Flowers, incense and light are the three classic offerings. You can add a small bowl of water (mizu 水) as an offering and a symbol of purity. Many people also have a small bell, the rin 鈴, whose sound marks the transition into practice.
The arrangement 配置
A simple arrangement works like this: the Buddha image stands in the middle and a bit higher, with light and incense in front of it, the flowers to the side and the water at the front. A small table or shelf is perfectly enough. More important than the furniture is that this place is reserved for your practice. In other words, no mail, no keys and no charging cables.
In a Shingon temple the arrangement is much more elaborate. The altar area is surrounded by the two great mandalas, and every ritual implement has its fixed place. You don't need to reproduce that at home, but it's good to know that nothing on a Buddhist altar is placed at random.
My advice is to start small, with one image, one candle and one stick of incense. The altar can grow along with your practice.
Altar and Reiki practice 実践
The altar is a good starting point for daily practice, whether that's Reiki, meditation or mantra recitation. You light the candle and the incense, put your hands together in gasshō, and begin. On days when motivation is low, lighting the candle is sometimes enough to get you going, because habit carries you when willpower wavers.
What else you put on your altar is up to you, for example images of the Buddhas and bodhisattvas you've been initiated into, or a mantra you've written yourself in calligraphy. There's no right or wrong here, only what supports your practice.

What an altar is not 注意
An altar isn't a display case to show visitors how spiritual you are. It's there for you and your practice. It's no coincidence that household altars in Japan often stand in a cabinet whose doors can be closed.
An altar isn't a magical object either. The power doesn't lie in the figure or in the candle, but in the regularity with which you sit down in front of it. And of course an altar isn't a requirement. You can practice Reiki without one. Many people who have tried it, though, wouldn't want to do without it anymore. What would be the first thing you'd put on your altar?
Your Path Into Daily Practice
An altar is a beginning. Daily practice with Reiki, meditation and mantra is what fills it with life.
Your Path in Shingon Reiki How a Session Unfolds