A completely handmade concrete masterpiece

On a sloped street in the Tokyo giant’s ward, an unusual building is surrounded by an office building and a looming crane accompanied by reconstruction. It is cleverly pieced together from lime concrete and looks out of place once and is perfect at home.

The Mita area it lives in was once the main real estate of powerful large or feudal lords; now, it is one of the most luxurious and upscale residential areas in the capital. In contrast to the unity, low-key affluence of neighbors, the primitive concrete walls of the small building are curvy curved, and the sloping windows seem to lean towards the city, as if listening. Instead, each surface of the structure is called the Arimasuton building (also known as the “Sagrada Familia of Mita”) with traces of hand, effort and improvisation.

For more than two decades, architect Keisuke Oka has poured his whole life into the building. It was often introduced as “handmade and built houses by himself”, but the architect quickly corrected the myth: it was a team effort. “My own imagination is limited,” he told TW. “It is by working with others that the doors keep opening up.”

Over the years, his friends, acquaintances and neighbors – musicians, students, architects, artists and countless others – have used this hand to construct Oka’s masterpiece, from custom windows to two doors on the ground floor. The result is a thoughtful structure, with many people’s labor, and full of what he calls “complexity and richness that is not easily decoded.”

Arimasuton: Uncategorized buildings

Even the building’s name evokes a clever sense of disease. In Japanese it is Arimasutonbiru – “Biru” means “build”. OK, a little bit. It combines the character “Ant” (Ari), “Trout” (Masu) and a raptor called the Black Kite (Tonbi), and the character “Ru” from Katakana. Its original handmade form resists the classification, inviting some to see it as an act of rebellion. In published articles Gekkan Arimasutonbiru Uri-Masu (Produced and sold online by Zine Oka) Guest writer Jun Yamaguchi describes it as “Anarchi Lecture”. Oka smiled in the semester, but made it differently.

“I do have anger about the way of building – the thinker and builder are completely separated, maybe a desire to resist this rebellion,” he admitted. “But it’s not just a rebellion, I want to make it clear: ‘It’s a good idea, isn’t it?’ If I can get empathy, and empathy can change someone’s actions, it will make me happy.”

The building is not an angry protest, but a debate raised in specific and time. In a world obsessed with novelty and stylish design, Oka shows that by adopting another natural and completely primitive way of thinking and making. “It is by ‘making’ human beings becoming humans rather than apes,” he said.

“The root cause of lying is human joy. For modern people who are stuck on smartphones and forget how to make things, I want to reawaken the joy among them.”

keisuke oka

Changes in the plan

In 2024, several media and architecture influencers on social media reported that Ali Marston Architecture is about to be completed. The scaffolding surrounding the building has disappeared, and Oka published the 22nd edition of his magazine – he was successfully placed in front of the finished building. But then, the bad news came. The surrounding area is in the middle of a massive reconstruction, and the structures on the sides of Arimasuton have been demolished, leaving it standing in a barren construction site. After a long and laborious negotiation with the real estate company, Oka has an option – the building must be 10 meters away from the reconstruction site.

Oka decided to move the structure through Hikiya, a traditional but technically complex technique that would keep him intact throughout the building, including its basement, during transportation. “I really hated the idea at first,” Oka admitted. The Arimasuton is precisely designed and is customized for the exact location where it stands. “The sloping windows, the way the landscape looks from the inside – each shape is determined in mind. If the position changes, the meaning is lost.”

But since then, he has maintained peace with the situation. “Because I’m building in the heart of the city, I always knew that rebuilding will come eventually. In that sense, facing and responding is the best route. And if redevelopment happens again in the future, I’ll have gone through a move – so I can move it again.”

Arimasuton Building is for sale every month

If the building itself is a dialogue between architects, communities and cities, then Oka’s magazine is its recording. Gekkan Arimasutonbiru Uri-Masu – It (very rough) translates to “the Arimasuton building for sale every month” – is a publication he started in 2022, a way to document and share the evolution of the project. Published monthly, only 150 copies, each question has a cover designed by others. Inside are the papers, updates and dispatches for the construction site.

Some cover photos show photos of Oka and his collaborators, using the tools at hand, dealing with structures or pausing smoke, while others feature fictional scenes that capture the spirit of the building in a more whimsical way. Together they form an inlay of perspectives, and everyone has glimpsed the arduous process that brought Arimasuton architecture to life.

By releasing new information every month, Oka hopes readers can feel the immediacy of the architecture and the feeling of what is currently being made. In a world where architecture is usually encountered only in smooth completions, he insists on showing an ongoing work – a little chaotic, continuous and full of life.

What does Oka want visitors to experience through his creations or when they walk in? His answer is simple. “I would be happy if I could spread the desire for creation.” The building is not to be in awe of the grandeur, but to inspire a quiet recognition—even in a society where “huge, narrow social feeling is impossible to touch”, there are some interventions to intervene.

A place to do something

In a near bright future, Oka intends to live in Arimasuton with his wife and rent it as a retail space. Eventually, he plans to sell it to people with will and resources to preserve the future. “If it could stay in a state where people can continue to see it, that would make me happy.”

After more than 20 years of history, Arimasuton Architecture reminds people that buildings can be individual, unpolished, collective, and of course deep humans. For young architects and self-builders, or just anyone who wants to create touch in an era of digital and fabrication, Oka has a simple message: “Believe in the little seeds that sprout in your heart. Cultivate them carefully and work hard until they emerge as truth in the world.”

He added: “If someone like me, not very good, can do this – then I hope others do more.”

More information

You can follow Keisuke Oka and keep up with the status of the Arimasuton building on Instagram and X, or check out his magazine here.

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