These gloomy citadels are just a concept design, one that imagines a massive defense network that could surround and defend Japan. Using a chain of breakwaters and drainage channels, these fortresses would protect the coast from tsunamis, while serving as an added layer of defense for man-made threats to the islands.
Victor Kopeikin and Pavlo Zabotin dreamed up this "Citadel Skyscraper" project. On the one hand, these buildings would function as medieval citadels, sitting out on the water and protecting the islands from any potential threats that might happen into their sea space. They imagine the buildings as self-sufficient residences, which would derive energy from the motion of the ocean, while housing agricultural spaces inside. (The architects also speculate that some of the population of Japan's crowded cities might move out to the citadels to create a little elbow room back on land.) On the other hand, the fortresses would form a defensive shield that could withstand waves up to 50-meters high and prevent those waves from reaching land.
It's not clear for what purpose Kopeikin and Zabotin created this concept, but it evokes an alternative timeline, one where Japan never opened its ports. Such a project, if undertaken, would be incredibly ambitious, but I wonder if it would really be possible to deflect tsunamis through this sort of engineering.
Citadel Skyscraper / Victor Kopeikin + Pavlo Zabotin [ArchDaily via WebUrbanist]