In all forms of Buddhism in Japan, the equinox is very significant. During the vernal (usually March 21) and autumnal (usually September 23) equinoxes, the length of the daylight and darkness in a day is exactly the same, and the sun rises due east and sets directly in the west. Nichiren Shoshu Buddhist Temples perform the Higan-e Ceremony on these days as a Buddhist practice for accumulating benefits and amassing virtue in the lives of the believer and the deceased.
The word “higan” is a translation of the Sanskrit word “paramita” and it means “arriving on the other shore.” It signifies “getting across.” Buddhism teaches that the world in which we live, called the impure world or saha realm (literally realm of endurance), is a place of suffering and troubles. In this schema, the saha world is located on this side of the shore. The source of all suffering — the three paths of earthly desires, karma and suffering — is likened to a great river. The life condition of enlightenment is likened to the other shore. In order to cross from the impure world, over the life and death sufferings of the great river, and reach the pure land on the other shore, people must embark upon the boat of the Buddha’s teachings.
Reference: Nichiren Shoshu Ceremonies book