This is a Hokkaido-only special edition of Black Thunder a popular chocolate snack. It is made with white chocolate in the company's Sapporo factory. The added copy reads "white thunder god" 白い雷神 (the thunder god is a Shinto-related god often seen in Japanese prints) and "Deliciousness straight down" おいしさ直滑降 (the word for straight down is most often used with skiing).
Black Thunder is the most well known brand from Tokyo based Yuraku Seika Confectionery company.
Key Words: Black Thunder, Yuraku Seika, ブラックサンダー ユーラク製菓