Torii (Torii/とりい) is one of the buildings in Japanese shrines. According to legend, it is a passage connecting the divine realm where gods live and the secular world where humans live, and is a kind of "barrier".
Why are most of Japan's torii gates red?
There is a saying that the Japanese have believed since ancient times that red has the power to exorcise demons, so the Torii gate is red. Also, red reminds people of blood flowing in the body and is adopted as a "symbol of vitality."
Perhaps for reasons like these, red is often used in sacred places such as shrines as a color that has the power to remove filth and bestow strength.