A U.S.-based social media challenge daring people to douse themselves with buckets of ice water has spread to Japan, with celebrities from billionaire Masayoshi Son to singer Ayumi Hamasaki taking up the gauntlet to boost awareness of what is known as Lou Gehrig's disease.

The so-called Ice Bucket Challenge campaign asks contenders to dump a bucket of ice water over themselves, post a video on social media, and then nominate three friends to do the same.

The nominees then have a choice. They can either take up the challenge or opt to make a donation to charitable organizations supporting the fight against Amyotrophic Lateral Sclerosis (ALS), a fatal neurodegenerative disease. They can, of course, do both if they want.