This time 12 months ago he was seeing out his days at Feilding High School and playing for the New Zealand Schools team.
He had dreams of being a builder and getting down to Dunedin to catch up with his good mate, Jona Nareki.
Wind on one year and his building days are no closer. But he is constructing a very impressive rugby career.
The 19-year-old has slotted into first-class rugby and is also gracing the stage on the sevens circuit around the world. He has played six tournaments for New Zealand on the world sevens circuit, performing in the all-important playmaker role for the New Zealand side.
Koroi, who was born in New Zealand to Fijian parents, said it all happened very fast.
"I did not see it coming. An opportunity comes along and I’ve got to take it with both hands," he said.
"For sevens, I knew Tomasi Cama. He asked me to come in. That opportunity came along and I took it. Otago came up and I was stunned about that . . . I had to pinch myself quite a bit, just remind myself that I’m not dreaming.
"It can be quite daunting. You are playing against people who you look up to, people you never thought you would play against or play with."
Koroi said he knew Cama, a former sevens star for New Zealand who had moved into coaching, through his older brother.
He ended up going to six sevens tournaments earlier this year — Sydney, Wellington, Las Vegas, Vancouver, Singapore and Hong Kong.
"I loved the travel. I went to places I never thought I would have gone to."
Vancouver was his favourite and he was happy to explore the cities when he was not training.
But sevens is on the backburner at the moment as the Otago season heads towards a climax.
"Just for the rest of the season I want to get some game time and keep performing — just make myself better.
"I have got a lot to work on. I’m only a young fella just out of school. But it is about making me feel comfortable and confident which Otago is trying to do.
"I’m just asking questions about what I have to do. My main goal is just positional awareness.
"Next year, I haven’t really thought about sevens at the moment. I’m just trying to focus on 15s here. [I] will just wait and see which way the wind blows me."
Koroi would start on the right wing for Otago today against Bay of Plenty, with his mate, Nareki, on the other wing.
The two have been friends since kindergarten and will be a dangerous combination for Otago this afternoon in what is a key match for both teams.
Otago has slipped to third after Manawatu picked up a bonus point on Thursday night in its close loss to Counties-Manukau.
If Otago can win well it can almost knock Bay of Plenty out of the playoffs but that is easier said than done.
Former Otago players Tom Franklin and Hugh Blake line up for Bay of Plenty, and lock Troy Callander attended Otago Boys’ High School.
Jono Ruru will start at halfback for Otago with Josh Renton moving to the bench in a late change as the home team looks for a fast start and a combative approach.
Mitre 10 Cup
Forsyth Barr Stadium, today, 2.35pm
Otago: Fletcher Smith, Vilimoni Koroi, Sio Tomkinson, Tei Walden, Jona Nareki, Josh Ioane, Jono Ruru, Mika Mafi, Dillon Hunt, Adam Knight, Josh Dickson, Josh Furno, Hisa Sasagi, Sam Anderson-Heather (captain), Craig Millar. Reserves: Sekonaia Pole, Aki Seiuli, Donald Brighouse, Joke Koroi, Slade McDowall, Josh Renton, Matt Faddes, Latu Vaeno
Bay of Plenty: Joe Webber, Monty Ioane, Lalakai Foketi, Terrence Hepetema, Chase Tiatia, Mike Delany, Richard Judd, Jess Parete, Hugh Blake, Tom Franklin, Troy Callander, Keepa Mewett (captain), Jeff Thwaites, Liam Polwart, Aidan Ross. Reserves: Seb Siataga, Jordan Lay, James Lay, Matthew Axtens, Ajay Mua, Luke Campbell, Matthew Garland, Elijah Nicholas
Referee: Ben O’Keefe (Wellington)