Buddhism was born in ancient India and migrated east; it later came to Japan via the ancient Korean kingdom of Paekche in the mid-6th century. “Incenses” were a part of a set of Buddhist teachings such as the scriptures, statues, and prayers. They were introduced as a means of purifying sins of this world with fragrance by carving and burning the aromatic woods. “Incenses” have been used for prayer from ancient times to present day. Incenses also became a part of everyday life and spiritual culture in general.
What we offer to the spirits of the deceased is called “Koden.” Originally, it meant to burn incense as an offering, but in the present day, it generally means gift-wrapping money. You can bring Koden anytime, but the first opportunity is at a wake. If you cannot be present for the wake, then you bring it to the funeral. It is customary to put the Koden envelope in a silk mourning cloth. Considering the original meaning of Koden, you can express your condolences more effectively by offering fragrant incense with it.
What are you supposed to do when you receive a card requesting you to refraining from sending New Year’s greetings at the end of the year, as you first learn of the death? You can express condolences more deeply by sending fragrant incenses with your sympathy and prayers. This is also called mourning get-well gift.
Obon is a merger of Buddhist beliefs with an ancient Japanese belief that spirits of ancestors return from the afterlife and spend time with their families (for three nights). It is a beautiful summer event held all over Japan, with the theme of expressing gratitude to ancestors and informing them of our well-being. In many places in Japan, Obon is held in August, but in Tokyo, it is held in July. In some areas, “Kyubon”, or the old bon, is held according to the old calendar. People wipe and purify gravestones and their family Buddhist altar, and offer elegant incenses, flowers, and other offerings to show appreciation and send prayers to ancestors.
Like a Obon, it’s the result of Buddhist teaching merging with ancient Japanese traditions of revering ancestors. For over a millennium, it has been twice a year in March and September on the spring and autumn equinoxes. The days are known as the equinox days of Ohigan. These are the days when the sun sets due west and we are directly connected to Amitabha's Buddhist paradise, where ancestors who have become spirits dwell. During Ohigan, you first make a visit to the cemetery and offer fragrant incenses and flowers.
We make offerings to Buddha in order to give form to our intentions and prayers. The smoke from incense connects us with Buddha and sends our prayers as we speak with Buddha in our hearts. Burning incenses is the same.
This actually varies depending on religious sects. Many sects offer three, but some offer only one. As far as burning incenses is concerned, three times is common, but some do it only once. There are no set rules to begin with and each sect developed its style throughout long history.
Incenses had an important role to play in celebratory occasions in the ancient times. You can find a detailed description of preparing celebratory incenses in the “Tale of Genji”, a story written during the Heian dynasty, when a princess of Hikaru Genji comes of age and becomes crown princess. Even in the present day, it is customary to offer incense to the family Buddhist altar of your in-laws to report that you are to become a part of the family. This has been passed down as a Japanese spiritual culture. Of course, the exact use varies from area to area.