With his face hidden behind sunglasses and a white surgical mask, the artist is almost as invisible as the radioactive contamination he is protesting against.
Yet his stickers are graphic reminders of the Fukushima nuclear disaster.
Known as 281 Antinuke, Japan's answer to Banksy has covered Tokyo streets in images depicting politicians as vampires and children being shielded from radioactive rain.
They are designed to highlight the consequences of the meltdown at Fukushima after the earthquake and tsunami in March, 2011. The disaster and the response by plant operator Tokyo Electric Power stoked anti-nuclear sentiment and the biggest public protests in Japan since the 1960s.
But the movement has since lost momentum.
"Perhaps because everyone believes people telling them on television that everything is fine, they don't seem so worried," 281 Antinuke said.
"I hope by leaving my art I can remind people we're not safe at all ... and that they will do something to protect themselves."
281 Antinuke is a rare presence in a country where graffiti writers face heavy penalties and strong social disapproval. Online commentators have called for his arrest and his agent says the artist has received death threats.
But he is determined to keep drawing attention to what he calls "an enormous public contamination disaster".
He said: "We don't know what will happen in the future, whether children will get cancer or leukaemia. So I want to keep making noise and making a fuss."
He does that under a shroud of secrecy. He refuses to provide any personal details, apart from the fact that 281 is taken from the number on his high school jersey.
The only clue to his age is a sprinkling of grey hair poking from under his hoodie.
Many of his bold designs depict children threatened by nuclear power, with the atomic symbol taking the place of flower petals, a biscuit or an inflatable swimming ring.
They are plastered on lamp posts and walls around central Tokyo, including the Shibuya entertainment district.
281 said he started dropping Antinuke from his moniker recently as he tackled topics such as an upcoming increase in consumption tax and Japan's hosting of the 2020 Olympics.
But he realises the risks in speaking out against the establishment and is careful to maintain his anonymity.
"My job is to add colour to things that are invisible," he said. "I don't think I should be seen."