Sandwiched between old residential apartments in the capital's central Minato Ward is the Arimaston Building, an eccentric collage of individually patterned concrete slabs piled upon each other as if by happenstance.

It's the work of Keisuke Oka, who has been building the unfinished structure mostly single-handedly, improvising as he goes. Some affectionately call him Mita's Antoni Gaudi, in homage to the building's address and the radically original Catalan architect known for his fantastical style.

It's become something of an attraction in the bustling office district interspersed by shiny high-rises and restaurant chains. Curious onlookers stop to take photographs of the peculiar gray mansion that has been featured in art exhibitions and magazines for its distinctive design and story, one that reflects Oka's own struggles as an architect searching for his brand of expression.