Box Boy & Box Girl Demo UPDATED
Nintendo have just published a Hako Boy！＆ Hako Girl！(Box Boy! + Box Girl!) demo on the Japanese Nintendo Switch eShop. The full game is also available to preload priced at ¥1,200, requiring 543 MB, and supporting English.
Edit: the demo is also availble in North America and Europe! Introduction video added below with the official website also now open.