The bird in the video is a White-crowned Sparrow, which are native to Northern Canada and the Western United States. There have only been 7 recorded sightings of White-crowned Sparrows in Japan, and this is the first time one has been seen on the island of Shikoku. The bird’s summer plumage is now visible, so observers expect that it will soon fly north and return to its home.
According to Wikipedia, this isn’t the first case of a White-crowned Sparrow migrating far from its natural breeding habitat. Vagrant White-crowned Sparrows have sometimes made their way to England and Ireland.