"I gave him a big hug, but you know, he is a typical teenager. I was proud," said the sushi chef, who completed his seventh ironman.
Crossing the line had been part of a two-year plan for Shotaro, who should this week find out if he has been accepted into the navy.
He competed in three half ironman events and finished the Auckland marathon last year as part of the build-up. He says his mum played a huge part in planning his path towards the big race.
A smile spreads across his face as he recalls the finish line.
"I was running in the dark and then there was the chute that was really bright. I was high-fiving people as I ran down. It was awesome. Dad was at the finish line and he said to me in Japanese, 'You are an Ironman'."
They helped each other during the 4km swim and came out of the water about five seconds apart, but over the bike and run legs Mr Hashimoto extended his lead.
Looking for a bigger challenge, Shotaro has set his sights on swimming the Cook Strait.
Ironman is a huge challenge and finishing an equally massive achievement.
And for Whangarei doctor and mother of three Denise Limby - in the 45-49 age group - making this year's start line was an achievement. Last year after months of training she was forced out of the race after she injured a disc in her neck while out running.
"I'm so glad I came back for another year. The run was fantastic because it was like a giant street party in Taupo.
She said it was a special moment crossing the finishing line with the jubilant crowd cheering and clapping.
"I've never done anything like it before."
The satisfaction of finishing Ironman makes NorthTech science tutor Toni Daly bubble with enthusiasm.
Two years ago swimming 300m was a huge challenge. But a determined and sustained effort to learn saw her cruise through the 4km swim leg at Taupo.
At home on her bike, Ms Daly - who was competing in the 50-54 age group - was happy smashing out the 180km ride.
She reckons her legs and lungs were fine during the 42km run and final leg of the race, but it was the huge blisters on her feet that slowed her up.
"I ran 20km and then I marched with enthusiasm to the finish," Ms Daly said.
Her next race is the Northern Crossing.