It offers tablets to replace the missing nutrients from foods such as hamburgers, pizza and ramen.
The pills are free, all customers have to do is trade in the receipt from their latest fast-food purchase, and each supply comes with professional advice about the health issues associated with these foods.
But the shop is not all it seems – the designers created it on behalf of Dohtonbori, a restaurant that sells organic, healthy fast food.
Its aim is to educate people and discourage them from choosing non-nutritional meals.
"This shop doesn't look like other pharmacies, but the truth is it's an educational supplement shop," explained Ikkyu.
"We opened this shop in Harajuku, where there are a lot of young people who have a bad eating habit," he continued.
"Once they get in, they are surprised with the the supplements they have to intake and they understand how bad their itching habit is."
In the shop's window, pill pots are lined up in rows beneath an illuminated sign that reads "For FREE".
This arrangement continues inside, where long shelves are mounted against wire fencing along the side walls. A counter stands in front of the tile-covered rear wall, while other details include a yellow neon cross and dispensers filled with more colourful pills.
The designers wanted the space to feel as clinical as possible, "like an antiseptic room".
"We created the shop design by coexisting the street atmosphere and a mad laboratory atmosphere," said Sato.
Fast Food Aid initially opened at the end of May for a trial period of just a week. It is currently closed, but the aim is to reopen it imminently on a more long-term basis.