On a sloped street in Tokyo\u2019s Minato ward, hemmed in by office towers and the looming cranes that accompany redevelopment, stands an unusual building. Artfully cobbled together out of stone-gray concrete, it looks at once out of place and perfectly at home.<\/p>\n
The Mita district in which it resides was once prime real estate for the powerful daimyo, or feudal lords; now, it\u2019s one of the most lavish and upscale residential areas of the capital. In contrast to the uniform, understated opulence of the neighborhood, this small building\u2019s raw concrete walls curve oddly, punctuated by slanted windows that seem to lean toward the city as if listening in. There is no neat symmetry, no glossy facade. Instead, every surface of the structure known as the Arimasuton building \u2014 also fondly referred to as the \u201cSagrada Familia of Mita\u201d \u2014 carries traces of hands, effort and improvisation.<\/p>\n
For more than two decades, architect Keisuke Oka has poured his entire life into the building.\u00a0 It\u2019s often introduced as the \u201chouse Oka built by hand and by himself,\u201d but the architect is quick to correct the myth: It\u2019s been a team effort. \u201cMy own imagination is limited,\u201d he tells TW. \u201cIt was by working with others that doors kept opening wider.\u201d<\/p>\n
Over the years, his friends, acquaintances and neighbors \u2014 musicians, students, architects, artists and countless others \u2014 have lent a hand in constructing Oka\u2019s masterpiece, from the custom-made windows to the two doors on the ground floor. The result is a structure that feels dense with thought, layered with the labor of many, and full of what he calls a \u201ccomplexity and richness that can\u2019t easily be decoded.\u201d<\/p>\n
Arimasuton: An Uncategorizable Building<\/p>\n
Even the building\u2019s name evokes a sense of artful disorder. In Japanese, it\u2019s Arimasutonbiru \u2014 with \u201cbiru\u201d meaning \u201cbuilding.\u201d Well, kind of. It combines the kanji characters for \u201cant\u201d (ari), \u201ctrout\u201d (masu) and a type of raptor called the black kite (tonbi), plus the katakana character for \u201cru.\u201d Its raw, handmade form resists categorization, inviting some to see it as an act of rebellion. In an essay published in Gekkan Arimasutonbiru Uri-masu (the zine Oka produces and sells online), guest writer Jun Yamaguchi described the building as \u201canarchi-tecture.\u201d Oka smiles at the term but frames it differently.<\/p>\n
\u201cI do have a kind of anger at the way architecture is done today \u2014 where thinkers and builders are completely separated \u2014 and maybe a desire to rebel against that,\u201d he admits. \u201cBut more than rebellion, I want to clearly show: \u2018This is a good idea, isn\u2019t it?\u2019 If I can gain empathy, and that empathy can then change someone\u2019s actions, that would make me happy.\u201d<\/p>\n
Rather than an angry protest, the building is more like an argument made in concrete and time. In a world obsessed with novelty and sleek design, Oka shows that by adopting a different way of thinking and making, something natural and wholly original emerges. \u201cIt was through \u2018making\u2019 that humans became human rather than apes,\u201d he says.<\/p>\n
\u201cAt the root of making lies fundamental human joy. To the modern people who are glued to their smartphones and are forgetting how to make things, I want to reawaken that joy in them.\u201d<\/p>\n
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Photo by Keisuke Oka<\/p>\n
A Change in Plans<\/p>\n
In 2024, several media outlets and architectural influencers on social media reported that the Arimasuton building was nearing completion. The scaffolding encasing the building had vanished, and Oka published the 22nd edition of his zine \u2014 with him posing triumphantly in front of the finished building. But then, bad news arrived. The surrounding area was in the midst of large-scale redevelopment, and the structures flanking Arimasuton were all torn down, leaving it standing in a barren construction site. After a long and laborious negotiation with the real estate company, Oka was left with one option \u2014 the building would have to move back 10 meters, away from the reconstruction site.<\/p>\n
Oka decided to move the structure through hikiya, a traditional but technically complicated technique that would allow him to keep the entire building, including its basement floor, intact during transport. \u201cAt first, I really hated the idea,\u201d Oka admits. Arimasuton had been designed precisely, custom-made for the exact spot in which it stood. \u201cThe slanted windows, the way the scenery looks from inside \u2014 every shape was determined with that place in mind. If the location changes, the meaning is lost.\u201d<\/p>\n
But he has since begrudgingly made peace with the situation. \u201cBecause I built in the center of the city, I always knew redevelopment would eventually come. In that sense, facing it now and responding is the best course. And, if redevelopment happens again in the future, I\u2019ll have already experienced moving once \u2014 so I can just move it again.\u201d<\/p>\n
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Arimasuton Building for Sale Monthly<\/p>\n
If the building itself is a dialogue between architect, community and city, Oka\u2019s zine is its recording. Gekkan Arimasutonbiru Uri-masu \u2014 which (very roughly) translates as \u201cArimasuton Building for Sale Monthly\u201d \u2014 is a publication he began in 2022 as a way to chronicle and share the project\u2019s evolution. Published every month on the 26th and limited to only 150 copies, each issue features a cover designed by a different person. Inside are essays, updates and dispatches from the building site.<\/p>\n
Some covers showcase photographs of Oka and his collaborators with tools in hand, working on the structure or pausing for a smoke break, while others feature illustrations with imaginary scenarios that capture the building\u2019s spirit in a more whimsical way. Together, they form a mosaic of perspectives, each offering a glimpse into the painstaking process that has brought the Arimasuton building to life.<\/p>\n
By releasing fresh information each month, Oka hopes readers can feel the immediacy of construction and the sense of something being made in the moment. In a world where architecture is usually encountered only in glossy completion, he insists on showing a work-in-progress \u2014 a bit messy, continuous and full of life.<\/p>\n
What does Oka want visitors to experience when they pass his creation or step inside? His answer is simple. \u201cIf I can spread the desire to create, I\u2019ll be happy.\u201d The building is not meant to awe with grandeur but to spark a quiet recognition \u2014 that even within a \u201chuge, constricting society that feels impossible to touch,\u201d there are ways to intervene, to leave a mark.<\/p>\n
A Place To Feel Like Making Something<\/p>\n
In the near-ish future, Oka intends to live in Arimasuton with his wife and rent the ground floor out as a retail space. Eventually, he plans to sell it to someone with the will and resources to preserve it for the future. \u201cIf it can remain in a state where people can continue to see it, that would make me happy.\u201d<\/p>\n
After more than 20 years, the Arimasuton building is a reminder that architecture can be personal, unpolished, collective and, of course, deeply human. For young architects and self-builders, or just anyone who wants to create something tactile in an age where everything\u2019s digital and fabricated, Oka has a simple message: \u201cTrust the small seeds that sprout in your heart. Nurture them carefully, and work them until they emerge in the world as truth.\u201d<\/p>\n
He adds, \u201cIf someone like me, not very remarkable, could do this much \u2014 then I want others to do far greater things.\u201d<\/p>\n
More Info<\/p>\n
You can follow Keisuke Oka and keep up with the status of the Arimasuton building on both Instagram<\/a> and X<\/a>, or\u00a0check out his zine here<\/a>.<\/p>\n Related Posts\u00a0<\/p>\n Kioi Seido: Tokyo\u2019s Enigmatic \u2018Building With No Purpose\u2019<\/a> Discover Tokyo, Every Week<\/p>\n Get the city’s best stories, under-the-radar spots and exclusive invites delivered straight to your inbox.<\/p>\n
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