Thirty-four-year-old Takeshi Inoue struggles with many of the daily tasks most people don't think twice about.
He can't read newspapers, or even street signs, and he doesn't know how to write his address.
When Inoue was nine years old he was diagnosed with diabetes and missed a lot of school. Then his mother got sick and he had to take care of her, which disrupted his education even more.
Now he's trying to fix that. He goes to evening classes, where he studies from an elementary school textbook.
Inoue says many people have no idea about his problem. "When I'm talking, it's hard for anyone to see the issue. I don't think I'm the only one struggling with this in Japan."
But nobody really knows. The last nationwide literacy survey was conducted back in 1948.
The Allied Forces were occupying Japan at the time, and were looking at reforming the education system so they wanted to know how many people could read and write. They found that more than 97 percent of the population could.
Though there is no up-to-date government data, there are signs that illiteracy may be more common than Japanese people believe. The most recent census, conducted nine years ago, found that more than 128,000 people had left school by the age of 12, some because of domestic abuse, some because of illness.
And the illiteracy issue isn't just about Japanese people who missed out on schooling. The foreign population is growing, and many people from abroad struggle to read or write Japanese.
One teenager from Nepal, who asked not to be named, came to Japan two years ago and enrolled in junior high school. But he wasn't able to communicate with his teachers or classmates.
"I was thinking I could learn Japanese from scratch, but no one taught me that at school," he says. So now he attends evening classes to catch up, and says he hopes to go to high school and then university, and eventually find work with a Japanese company.
Foreign illiteracy is a problem likely to grow as Japan welcomes more foreign workers to help deal with a severe labor shortage. The government has introduced a new work visa program it says will attract around 345,000 people from abroad over the next five years.
People who miss out on education can turn to government-run evening schools. But they operate in only 9 of Japan's 47 prefectures. Volunteers are running evening classes to help fill the gap, but one of the teachers, Nobuhito Shironouchi, says illiteracy is a lot more common than most Japanese people believe.
Hiroshi Noyama, Associate Professor at the National Institute for Japanese Language and Linguistics, is trying to put a figure on it.
He leads a team of researchers planning to assess how well foreigners and Japanese people who attend evening classes can read and write.
The idea is to determine roughly how extensive the problem is, get the government to launch a national survey, and help create a roadmap to resolving the issue.
Noyama says learning to read and write allows people to live full lives, protect their rights and stay safe. "It's important to find out what needs to be done to ensure everyone living in the country can read and write Japanese, at least at a basic level," he says.