She had no chance, her Hobart-based daughter says.

When the 18-metre wave hit, all three – as well 10 of Ms Otsuka's closest friends – were swept away.

"She didn't know what to do. No one did," Ms Otsuka says.

The grandmother had heard the warnings that were broadcast three minutes after the magnitude nine offshore earthquake hit at 2.46pm on March 11, 2011. The first alarm warned of a three-metre tsunami. From about 3.15pm, walls of water up to 40m high crashed with Tohoku's coastline, sweeping cities, villages, 350,000 buildings and 18,465 lives away in moments – 1028 of the Kesennuma's 70,000 people were killed. More than 300 more went missing.

About 250 kilometres south, the Fukishima Dai-Ichi Nuclear Power Plant fast approached the full nuclear meltdown that led to the evacuation of more than 450,000 people.

The Great East Japan Earthquake is still felt every day. As of January, 182,000 people remain in temporary accommodation. Tourism is at 62 per cent of its pre-quake levels. By last year, just 19 per cent of "town development" had been completed.

Aerial photos show vast swaths of Kesennuma that lie bare, their former communities and homes erased. In small pockets, neat mounds of earth have appeared, raising the land height by eight metres.

But perhaps most striking are the vast walls of concrete that now choke small harbours, tower over homes and obliterate beaches as part of the Japanese government's mission to defend the coast of their nation.

In 2011, a shocked leadership did what it felt it must to protect its reeling people, adopting a grand plan to "fight" the force of nature.

Within months, plans to build super seawalls of up to 17m in height along more than 400km of the coastline of the worst-hit Fukishima, Miyagi and Iwate prefectures at a cost of $US10 billion were approved.

The eventual aim is to stretch Japan's seashore fortifications from a pre-existing 9500km to cover 14,000km of its entire 35,000km coastline.

But seawalls are dividing more than the ocean and the land as locals vow to learn from the lessons of 2011.

"In the immediate aftermath of the earthquake, the idea of protecting the land with giant structures became a kind of symbol," says Associate Professor Satoquo Seino of Kyushu University's school of engineering.

"The academic community was unable to sufficiently discuss and offer advice. The atmosphere was that doubts raised about building infrastructure designed to save lives were interpreted as taking human life lightly and questioners were bashed," she said via email.

It is exactly these doubts that are at the heart of a group of academics led by Melbourne's RMIT University and funded by the Australian government and the Japan Australia Foundation.

"My concern is that it's a huge environmental disaster to build these enormous structures that provide a false sense of security," says RMIT landscape architect Marieluise Jonas.

Quite apart from slicing through communities, ecosystems and tourist spots, experts doubt the seawalls will be any match for a tsunami of the magnitude of 2011's once-in-a-1000-years nightmare.

Seawall advocates point to the village of Fudai, where 3000 people escaped the perils of the mega tsunami thanks to a 15m wall and floodgates that were built – and largely ridiculed – in the 1970s. Yet, not only was Fudai spared the largest surge, but none of the new seawalls come close to reaching the 40m needed to have any hope in a replay of March 11. That day's onslaught smashed through 90 per cent of Tohoku's pre-existing seawalls. Kamaishi's 10m walls, then the largest in the world, simply crumbled on impact.

Ms Otsuka, a Japanese teacher and seawall opponent, cites figures that showed death rates in seawall-free settlements were a quarter of those where walls existed.

"What we say is whenever there is a big earthquake, just run away. There is nothing that stops it. If you don't feel that sense of urgency, you don't run," says Ms Otsuka, who believes that had her family known to climb 10m up a hill behind her mother's home, they would have been spared.

Working alongside Dr Jonas, she is educating Kesennuma locals around disaster risk reduction, an effort that she says is "purely" about the memory of her deceased family and friends.

"I'm extremely sad and resentful of the fact that the recovery program is creating even more danger for the people. Someone has to tell the world in order not to repeat the mistakes that my mother made," says Ms Otsuka, who helped organise Kesennuma's Future Proofing workshop in January.

Indeed, many of those who died five years ago had run towards seawalls – and some of those had watched from atop the walls as the wave approached.

Not that all seawalls sit near communities. In the village of Koizumi, 40 of 1800 residents died. Now rehoused uphill and 3km inland, survivors can visit a bare patch of scrub where their village used to sit. Where there was once a sea view is now a 14.7m, 2km-long concrete wall. At a cost of $440 million of central government funds, the edifice defends rice paddies and not a single building – or human – whatsoever.

Given the local government has set aside less than one-third of that to help Kesennuma's now-homeless residents relocate, says Ms Otsuka, the imbalance is "staggering".

Just as Fudai is held up as an exemplar of man's dominance over mother nature, Okushiri Island has come to illustrate the ecological folly of many thousands of tons of concrete sitting on a seashore.

There, the small island's population has diminished in line with the local fishing and tourism industries, which have shrunk by 50 and 30 per cent respectively since seawalls were built after the 1993 tsunami. With run-off from the hills to the sea obstructed, the waters have lost nutrients and reefs have silted up.

"This island used to be called the Island of Treasure because of the high price of abalone and urchins and they just disappeared," Ms Otsuka says.

The very fishermen the walls were built to protect have had their livelihoods slowly, painfully eroded.

In Prime Minster Shinzo Abe, the structures have support from the top. His position speaks of a long and deep connection between the government and construction mandarins. So ingrained is that relationship, says Dr Seino, that the construction industry is preserved as a kind of reserve corps in a country prone to natural disasters.

Protesting the walls' march is not popular for other reasons, too. Without the structures, local government will not go ahead with any rebuilding, a technicality that has been played off against communities which have an understandable desire to get on with life.

In parts of Kesennuma, virtually nothing has moved forwards. A high school building sits as it was on the day of the tsunami, debris included.

Yet one of the plan's most prominent detractors is also Mr Abe's wife, Akie Abe, who has tapped into the traditional belief that forests are the friends of the sea. Mrs Abe's support may be something of a win for campaigners, though it's unlikely the PM will bow to protest – or indeed, Australian academics.

Dr Jonas points to historical architecture and habits that may benefit a new Kesennuma. But the most sensible solution, she says, is the simplest: Move uphill.

Residents such as Keiko Sugawara, whose family survived, albeit frostbitten, say she has never had input into the plans.

"The tsunami itself was a natural phenomenon but the disaster was man-made," she says via email. "It is just impossible for me to stay silent … I feel such a sense of threat that we are inching our way towards the disappearance of the future of this town.

"If there is no reconsideration of this, the coastline of Japan will become a sight that is too terrible to bear."

With the community and its leaders racked by post-traumatic stress disorder, careful, participatory decision-making should be undertaken, Dr Seino says.

One of Future Proofing's most positive outcomes, says Dr Jonas, was sharing experiences learnt by women's groups after Queensland flooding and Tasmanian bushfires. When Australian women banded together, they could not have known their strength would go on to inspire women facing similar upheaval in Kesennuma.

And they might understand better than most that at the heart of campaigners' arguments is something far less tangible than death tolls and poured concrete.

The sea is not only part of Tohoku's famed, island-dotted coastline, it is part of the Japanese spirit.

"After the tsunami, after all that loss, we couldn't hate the sea," says Ms Otsuka.

"That's where our energy comes from, it's a blessing, not a resource. The tsunami didn't destroy our soul but this plan has," her voice breaks. "It's nothing like the town that we had before, that we always loved and gave us energy. It's monstrous."

Dr Jonas will be presenting AfterLandscapes: Designing in Uncertainty at the Japan Foundation on March 18.