Final answer:
Mahayana Buddhism is the most popular sect of Buddhism in Japan, encompassing various forms including Zen Buddhism, and known for its emphasis on meditation and universal compassion.
Step-by-step explanation:
The most popular sect of Buddhism in Japan is Mahayana Buddhism. Within Mahayana, there are various forms, including Zen Buddhism, which is known for its emphasis on meditation and is widely practiced in Japan. Mahayana Buddhism is characterized by universal compassion, altruism, and selflessness, and it is considered compatible with other religious beliefs. This sect is not only the predominant form of Buddhism in Japan but also in other East Asian countries such as Taiwan, Korea, and parts of China and Vietnam.