More than 6,000 fans packed into the stadium, which will host two matches during the 2019 tournament and has been built on land that was previously the site of the local school that was wiped out by the tsunami seven years ago.
The children's decision to race for higher ground meant every single student at school that day survived and many of them were in the ground on Sunday.
Kamaishi lost 1,145 of its citizens in the wake of the tsunami and was chosen to be a World Cup city as a symbol of Japan's desire to use the tournament, as well as the Tokyo 2020 Olympics, to promote reconstruction in the area.
However, Kamaishi is also historically a rugby town. There has been a professional rugby team there since 1959 and Nippon Steel Kamaishi, who would eventually become the Seawaves, won seven national championships from 1979-85. The new stadium will be their new home.
KAMAISHI IS READY
On Sunday, the Seawaves faced Yamaha Jubilo, a poignant fixture given the history shared between the two sides.
Just months after the tsunami destroyed most the town, Yamaha were the first team to visit the area in a fixture against the Seawaves charged with emotion.
Sunday was an emotional day too, but for drastically different reasons, as officials, players and local residents spoke of the hope that the stadium represents.
Following a poignant rendition of the school song performed on the pitch, 17-year-old student Rui Horaguchi addressed the crowd before breaking into English to send a message to the world that Kamaishi is ready.
"Thank you everyone for all your support. We have recovered and are looking forward to welcoming you," said Horaguchi.
The festivities featured a performance from J-Pop band Exile, as well as a host of Japanese rugby stars, including 2015 Rugby World Cup hero Ayumu Goromaru who was instrumental in Japan's historic win over South Africa in that tournament.
Goromaru, who was injured so couldn't play for Yamaha, said it was important to all of Japanese rugby to come back to Kamaishi.
"Being able to be back here today is really important thing for us to be involved in," he said on the sideline of the pitch.
"Going forward, in terms of the recovery ahead of the World Cup, we want to be as involved as possible.
"For Japan as a whole, the earthquake was a huge shock so to have this stadium here now is a real sense of history. I hope many people from overseas have a chance to visit."
Yamaha may have won the match, 29-24, but the result seemed meaningless given the significance surrounding the event.
As the crowd slowly moved away from the stadium, 30-year-old Keiko Yamashita summed up the mood perfectly.
"Rugby isn't everything, it is just a game," she said, dressed in a souvenir Kamaishi rugby shirt.
"But sometimes what people need is a game to remind them of what is good and that is what happened here today. We were reminded of what is good."
(Reporting by Jack Tarrant; Editing by Christian Radnedge)
