Japan is one of the fastest-ageing societies in the world, with almost a third of its population over 65 years old. As a result, the county is seeing more and more cases of dementia each year: almost 5 million people are now living with the condition. In response, the government is taking the problem seriously and has formed a special committee in a bid to tackle the crisis. Our correspondents Alexis Bregere, Mélodie Sforza and Justin McCurry report from Tokyo.