Numbers as of December 31, 2024. From the Religious Yearbook 2025 (Agency for Cultural Affairs).
Buddhism in Japan came from India by way of China and the Korean Peninsula.
Its official arrival is said to be in 538 (one view says 552). Even before that, people who came from the continent had brought it among ordinary people.
Nara Buddhism was brought by monks who came to Japan and by envoys to Tang China. Saicho and Kukai brought Tendai and Shingon from Tang China and founded them in Japan.
Until the early Kamakura period, Japanese Buddhism was thought to have eight schools: the six Nara schools (Sanron, Jojitsu, Kusha, Hosso, Kegon and Ritsu), and Tendai and Shingon.
In the Kamakura period, Japanese people founded their own forms of Buddhism: Honen’s Jodo-shu, Shinran’s Jodo Shinshu and Nichiren’s Nichiren-shu.
In the same period, Eisai and Dogen, who had studied in Song China, brought Rinzai and Soto Zen to Japan.
Before the Religious Organizations Law of 1939, 13 Buddhist sects with 56 branches were officially recognized. In 1939 they were brought together into 28.
As of December 31, 2024, there were 76,493 Buddhist religious corporations, and Buddhist groups reported 80,463,918 followers. Shinto groups reported 86,359,612, out of a total of 175,054,047 followers for all religions.
There is no single right answer. Talking it over with someone at home is a good way to learn.