Shinsosai exists because a political argument made it necessary. From the eighteenth century, nativist scholars in the kokugaku movement argued that Japanese should be buried by Japanese rites rather than by an imported religion, and worked out funeral orders from classical precedents and from the practice of a few priestly houses that had kept their own. Some domains permitted Shinto funerals for shrine priests before the Restoration.
The Meiji government took the argument up. Its separation of Shinto from Buddhism after 1868 required Shinto to be able to do what Buddhism did, and for a period in the early Meiji years Shinto funerals were actively promoted and in some places imposed. The promotion did not hold. Buddhist funeral practice was too deeply established in family and parish life, the new rite had no comparable network of temples and graves behind it, and the state changed course. What survived is a real but minority form, kept by shrine families, by some Shinto-derived new religions, and by households that choose it.
The service itself is held at home or in a funeral hall rather than at a shrine. Its stages parallel the Buddhist sequence, with offerings of food, sakaki branches presented in place of incense, and a norito-style address rather than sutra chanting. The dead person is not given a posthumous Buddhist name; they are installed as a spirit of the household, honoured at a spirit shelf in the home on set days and thereafter as an ancestor of the family.