"One thing I learned very quickly when I got here was the English banter," said Harrison, who is ending an 11-year spell in Northampton this summer as he heads to France to join Pro D2 side Provence.
"I remember I got off the plane, Dusty (Hare) picked me up, we drove to the club and I was greeted by Nick Johnston.
"Dylan (Hartley) was showing me around and we ran into Nick. He was like 'f*****g hell, you're going to get some s**t with that haircut, mate - you look like a blancmange'.
"I looked at Dyls and I was like 'do I fight this guy, is he taking the p**s out of me, am I supposed to swing?'.
"I wasn't used to anything like that, and Dyls was like 'it's just bants, bro - you'll get used to it'.
"Anyway, Nick was a cool guy and I got on really well with him, we laughed it off, but it was a bit of a shock coming into an environment like that."
Johnston was notorious for the tough pre-season training that he put the Saints players through, giving Harrison, who arrived completely raw from New Zealand, a full-on culture shock in his first venture into professional rugby.
"I remember one of the sessions we went out to Everdon and we were running up cow hills," he recalled.
"If you looked at it now, it was so behind the times but they were all about your mentality, no matter how hard it was you just get through it.
"We had a heard of cows come stampeding through us and Nick Johnston is yelling 'cows, run!'.
"Alex Day passed out on the hill because it was 30 degrees and he had to have oxygen as a first-year Academy player.
"Out of about 10 first-team Academy boys, I think about seven of them got injured pretty seriously.
"It was all just mental toughness really, just getting through it, but as a young fella you sort of need that and I definitely appreciated that!"
Director of rugby Jim Mallinder and forwards coach Dorian West were the main men at Saints at that time.
And if Harrison thought Johnston was no-nonsense, West was clearly on another level.
"Meeting Westy, I showed up with half a head full of dreads (dreadlocks)," Harrison explained.
"I remember playing a couple of games for the Wandies and I thought I played pretty well, obviously well enough to get a contract but Westy pulled me in at the end of the season and said 'I really want that hair gone'.
"I was like 'right' and I thought he was joking.
"I went off, had my off-season and came back, and he said 'I see you still haven't cut that 'f*****g' hair, I laughed it off again, but the third time he pulled me in, he said 'no, I'm being serious, cut your hair, you want to be known for your rugby not your haircut, otherwise you won't play under me'.
"I cut my hair, cut it all bald, and funnily enough I didn't play for the rest of the season any way so I cut it for no reason!
"Westy was probably a big part of my character building, it was pretty tough love with him, relatively straight up and down.
"The thing that he liked about me was the grit, I dug my teeth in, didn't take s**t and I ran into brick walls for him so that helped me out.
"His famous saying was 'you'll be alright, get some pills and tape and soldier through'.
"I was a part of that and I was numbing the AC joint in my shoulder every week just to get through.
"We weren't playing easy games as well, I was doing it through Champions Cup and things like that.
"I enjoyed working with Westy. There was a bit of a love-hate thing when he wasn't picking me."
One thing Harrison struggled to understand at times was the lack of freedom forwards were given.
"The one thing I didn't really appreciate was them not wanting you to do out-the-back passes and showboat a bit," he said.
"I was here towards the end of Westy and Jim but when I first showed up, forwards were not expected to pass, they would carry straight and hard and backs would do all the fancy stuff.
"The year that I came (Harrison made his debut against Wasps in March 2012), it was pretty clear that the teams that were doing really well were the ones who played as we do now.
"I remember Louis Picamoles came over and he was the only one (forward) who was allowed to do anything flash. He was the only one allowed to offload, throw balls out the back.
"I'd seen a couple of forwards kick the ball, and they didn't play the next week because they kicked the ball.
"In our game against Newcastle recently, Juarno (Augustus) kicked the ball and Skos (Courtnall Skosan) scored off it, Colesy (Alex Coles) kicked the ball, hell of a kick and Sammy Matavesi kicked the ball and scored so that goes to show how far Northampton Saints' game has progressed.
"I guess that is down to the players we've got and Boydy (Chris Boyd) giving us license to play what's in front of us.
"I think Jim and Dorian did try to change towards the end and it made a difference but the boys probably weren't used to playing that way."
When Harrison first arrived at Saints, you would think he may have been intimidated by the players he was competing against for a position in the back row.
Saints had reached the Heineken Cup final in 2011, losing to Leinster in a galling showpiece in Cardiff.
The black, green and gold had assembled the most ferocious pack in Europe, stomping on all before them before the eventually ran out of steam in the second half of the final.
But Harrison had no idea what he was letting himself in for when he arrived towards the end of 2011.
"The boys playing in the back row were Woody (Tom Wood), Calum Clark, Roger Wilson, Dows (Phil Dowson) so there was a lot of quality there," he said. "But coming over, I was pretty naive - I didn't watch any English rugby.
"I knew Courtney (Lawes) and Woody and Dyls through England playing against the All Blacks and that but I didn't have an idea of how good these guys were.
"I came over pretty confident I could make something happen and I always thought to myself I wonder if I'd have got more of an opportunity as a young fella if it was under Boydy.
"I feel that Westy especially didn't play the young guys as much as he could have. After the game I could guarantee you I could pick the team for next week, whether we lost or did well.
"Me and Ben Nutley were playing really well for the Wanderers week in, week out and I remember going to chat to Westy and I said 'I don't expect to be starting, but when do I get a shot? I'm playing really well'.
"His response to me was 'you're probably one of the best ball carriers in the squad, but you're not a lineout option'.
"So I went away and worked on my lineouts and I wasn't the best lineout option but I could do a job.
"I went back to him and he said 'you've done that but you can't play eight, we need someone that can cover eight'.
"So I said 'can I play eight in a Wanderers game?' and he said 'no, we don't see you as an eight'.
"How funny is it that I became an eight in my career?
"Sam Dickinson got injured, it forced me into that eight position and the rest is history."
As he references, Harrison eventually forced his way into the first-team picture.
Having only started eight times in four seasons prior to the start of the 2015/16 campaign, he suddenly became an integral figure.
In fact, so influential was he that he was named in the Premiership dream team for that season.
"I started the season at seven but we had a bad run of injuries that year," he explained.
"Calum Clark and Woody were injured so I played a good chunk at seven but then Sam got injured so I played half the season at eight.
"The next year they brought in Louis Picamoles so I vacated eight pretty quick!
"He left and they didn't really replace him so they left me in there. Happy days really."
Harrison did so well during that breakthrough season at Saints that England sat up and took notice as he qualified for the Red Rose through his father.
"The first game of that (2015/16) season was about my 20th for Saints and it was just a buzz being part of the first team," Harrison said.
"At the end of the season, people were saying I would go on tour but I was just happy to be playing for Saints.
"I got the England call and I was buzzing, it was a great experience and I really enjoyed it.
"But I think the way I train affected me - I don't like going hard at training - whereas Eddie (Jones) likes boys who are going to smash their mates in training.
"I've got something of a switch where I don't run hard in training but I can flick that switch for games.
"If you ask the boys, I'm probably one of the easiest guys to train against.
"There's a time and a place for it and I think that probably let me down at England training. I didn't adapt to it quick enough.
"It was an opportunity missed and I can't dwell on it too much."
Many reading this will be surprised that Harrison admits he is not a tough trainer as, watching him purely in matches, you could imagine him chopping down team-mates left, right and centre on the paddock.
After all, it was that ferocity that helped him catch the eye of Saints, and of Hartley, who noticed how good he was on a visit to the school they both attended, Rotorua Boys’ High School, during the 2011 World Cup.
"My coach at school coached Dylan in the first 15 and I had an English passport through my dad and he said to me 'that's the golden ticket, bro, because you don't count as an overseas player so clubs will automatically favour you'," Harrison said.
"He told me that if I wanted to pursue it he would put the feelers out, and I told him I would love him to.
"He messaged Dylan and said he had a young kid who was on the right track and asked him what the best club would be and how we could make it happen.
"Dylan told him Dusty Hare was the one to talk to and Dusty ended up saying he'd love to have me over for a trial.
"It all went quiet so I thought the opportunity had gone.
"Four or five months passed and I got a random message on Facebook from an agent and he told me he'd seen an article about me on the BBC and he wanted to represent me.
"I have absolutely no idea how that article happened because I didn't talk to anyone.
"He said he already had two clubs interested in me, one being Tigers and one being London Irish.
"I told him I'd previously had a conversation with Northampton Saints and asked him if he could get in touch with them.
"The next day he told me Saints were keen and the next day we had a big derby game at school and that was the game that Dylan came and watched.
"Dylan sat down with me and told me the club wanted me on a trial and it was unusual because they didn't just offer them out.
"He told me it could change my life. That was on the Saturday and then on the Tuesday he told me I needed to leave tomorrow.
"I hadn't even told my mum at this point, I rang her, she broke down in tears and they ended up paying for me to come over for a three-month trial.
"I got here and never looked back.
"I remember Dylan had an Xbox360 that was brand new at the time and he told me if I got a contract I could have that Xbox.
"So I was playing my heart out for an Xbox360, not knowing the decision to come over would literally change my life.
"I came over and lived with Alex Day, James Palmer and Danny Herriott.
"I was telling my boys at home that I was going to England to play for Saints and they were like 'bro, you're going to be on like 100 grand'.
"I was like 'wicked, wicked', but I got here and Dusty handed me 100 bucks and told me to come back next week and he'd give me another 100.
"I signed my first contract and it was for like five grand!"
But though that was not a lot of money, Harrison was just grateful for the opportunity, especially as he originated from Opitiki, an area of New Zealand where some were not so fortunate.
"My family is not well off, we live a comfortable life but I'm from 40 minutes out of the nearest town. I got what I needed, not what I wanted," he said.
"The biggest change was the lifestyle. Northampton to me is a big city, a big change.
"I was used to going home and going hunting and fishing, but here you go and drink coffee with your boys. It was a big culture shock.
"I'd been living away from home since I was 12 because I went to boarding school and it was such a good experience that set me up really nicely.
"I wasn't on a playing scholarship (at Rotorua Boys’ High School), I went there on a grant because my hometown is pretty dangerous, kids fall into the drug scene so the government give out grants based on where you are and the risk level of falling into gangs.
"I was quite lucky to stay there because it was quite an expensive school to go to."
Harrison had some tough times that gave him added mental fortitude during his youth.
And those things have driven him on, day by day, during his 185 appearances for Saints.
Harrison continues to honour the memory of a close friend, Bishop Thompson, who died in a tragic jet ski accident.
Harrison was one of two 18-year-olds to be convicted and discharged without further penalty for causing the death of Thompson on Lake Okareka, Rotorua, in 2011.
"At the time, you're fearless, you don't really think anything's going to affect you, you roll with the punches and when that happened it hit home," Harrison said.
"It showed you're not promised tomorrow and something could happen and that's you done. You have to take every opportunity as it comes.
"The whole time I've been playing, I've said to myself that I'm playing for the both of us.
"It was a hard time and I'm lucky I had good friends and family around me.
"It's something that's definitely driven me massively through my career and had a massive impact on the way I approach decisions."
Harrison would have a big decision to make 11 years later as he opted to end his successful stay at Saints for a move to Provence.
He discusses that, and much more, in part two of this special interview, which will be published next week.