When the earthquake struck, Jin Abe and his 80-year-old grandmother Sumi Abe were in the kitchen on the top floor of a two-storey wooden house.
The building collapsed trapping both inside, but the 16-year-old said he was able to reach blankets, food, and drink, helping them survive for about 10 days.
"We found some water and snacks, so we ate them," he said on Monday from his hospital bed in the devastated coastal city of Ishinomaki in Miyagi Prefecture.
"We heard people outside but we couldn't escape," he told reporters. The teen explained that he and his grandmother had huddled together to keep warm, but were unable to stand up or walk around.
On Sunday he managed to dig out from some of the rubble and call out to rescue teams searching the earthquake and tsunami zone. Rescuers heard him and grandmother and teen were airlifted to hospital.