"He now plays 20 minutes at Manchester United on the left wing.

“My heart breaks. Really, I have tears in my eyes.

"He’s an offensive midfielder with one of the best noses for goal I ever saw."

There aren't too many Manchester United players Jurgen Klopp would rave about, but back in 2013 it was a very different story.

Long before the charismatic German went on to rile United supporters with his restoration of the red half of Merseyside he was making waves in his homeland, with an exciting Borussia Dortmund side who had knocked Bayern Munich off their perch.

Central to that team was the attacking talents of Robert Lewandowski, but arguably the greater force was the unassuming playmaker pulling the strings behind him: Shinji Kagawa.

Born in Kobe, Japan, Kagawa started playing football at the age of five, going through the ranks of his local youth sides before he was talent-spotted by Cerezo Osaka at the age of 17.

He'd spend four years at Cerezo and rise to prominence in 2009 when he finished as the top-scorer in the J League 2, the second flight of national football in his homeland.

Dortmund were one side alerted to his talents and moved swiftly to activate a €350,000 release clause in his deal which would allow him to leave the club with no questions asked for a shot in Europe.

Klopp had just led Dortmund to fifth in the Bundesliga, qualifying for the Europa League as a result, using the money to bring in Kagawa along with the likes of Lewandowski from Lech Poznan and Lukasz Piszczek from Hertha Berlin.

It was to be the perfect match for an exciting young manager and his exciting young squad as Dortmund raced to the Bundesliga title, with Kagawa named in the league's team of the season despite missing half the campaign through injury.

Shinji Kagawa was an instant impact under mentor Jurgen Klopp

The following season was to be even better as Kagawa returned from injury rejuvenated, helping Dortmund to a second successive title as they set a Bundesliga record for the most points across a single campaign.

His crowning moment would come in the German Cup final victory, grabbing a goal and an assist as Klopp's side thrashed Bayern 5-2 to complete an historic double.

Having won back-to-back league titles Kagawa was hungry for the next step in his career and his advisers had made him well aware of growing interest from the Premier League.

Ironically it was Liverpool, the next side Klopp would manage, who were hotly linked with a move while Arsenal and United were both also making their feelings known.

Of them all United remain the biggest side in Japan to this day and Kagawa knew who his preference would be, though he made it clear he wouldn't move to Old Trafford if he wasn't going to be playing on a regular basis.

“My first reaction was ‘Manchester United are bigger than Liverpool, Arsenal and Dortmund,'" Kagawa told The Athletic. "I waited for the offer; I really wanted to play for Manchester United even though I was happy at Dortmund.

“I wanted to talk to Ferguson face to face. I wanted to know if the offer was from United or from Ferguson and whether he wanted me. I also wanted to know where he wanted me to play.

“I met Ferguson in an airport. He told me what he wanted. I didn’t speak much English and he was difficult to understand, but the message was clear. I was certain that I wanted to play for United. Ferguson explained that he wanted to win the league back with me in the team. He wanted me to be a champion of England too.”

After the brutal agony of missing out on the Premier League title to Manchester City in the dying moments of the previous season, Sir Alex Ferguson demanded an immediate response from the United board.

Many fans point to Robin van Persie as the signing that would swing the pendulum back towards Old Trafford in the summer of 2012, though it was Kagawa who arrived first, joining shortly after young hopeful Nick Powell from Crewe.

Shinji Kagawa was unveiled as a new United signing on 22 June 2012

“The best surprise was when Robin van Persie arrived," he added. "The whole dressing room was like ‘wow’. We had great players, we knew we were good, but when Robin walked in he gave everyone a lift. He’s been the best goalscorer in England and we took him from a main rival. We were ready to be champions again.

“One-on-one, the players were better individually in Manchester. In Dortmund, we played as a team. In Manchester, it was more about individual talents. We had some of the biggest names in the world. Rooney, Van Persie, Giggs, Nani. Scholes was finishing his career but he was still top level. We played rondos. Scholes was never in the middle because he never lost the ball. Never.

“Giggs was older than Scholes, nearly 40, but still fast and skilful. He was super professional. We also had Ferdinand, Vidic, Evra. Three of the best defenders in the world.”

The respect was mutual for Kagawa, a player who impressed key dressing room figures at Old Trafford as soon as they were made aware of Ferguson's interest in the playmaker.

“I’ve been very, very impressed. I’d seen him play for Dortmund on TV and I looked on YouTube," Rio Ferdinand said while on a pre-season tour in Shanghai.

“He’s been fantastic. He’s quick, he’s sharp, he has great awareness, he plays off both feet. I’m excited about playing with him and getting the season started.

“He’s been one of the better players in Germany for the last few years. I think he will bring that form to Manchester United. I think he’ll be a great acquisition.”

Yet at first there was an air of cynicism regarding the £17million move for Kagawa, with some critics suggesting he had simply been signed in order to tap into the huge Asian market possessed by the club.

"Our popularity in certain countries or regions may depend, at least in part, on fielding certain players from those countries or regions," then-commercial director Richard Arnold insisted.

"We don't sign players to sell shirts. We are reliant on 25 players and they are all massive stars. We have 25 George Clooneys."

Japanese fans welcome Shinji Kagawa during an Olympic football match played at Old Trafford

Kagawa would certainly help boost those merchandise sales when he netted his first goal in a pre-season friendly against Shanghai Shenhua, but on the opening day of the season Ferguson would put his full faith in the Japanese playmaker with a start against Everton in a disappointing 1-0 defeat.

Despite the early setback the summer signing would start again for the second home match, grabbing his first competitive goal for the club on the same day Van Persie got his in a 3-2 win over Fulham.

“I was against Mousa Dembele, a very good and strong player," he said of his debut. "It was tough, we won 3-2 and I went home thinking: ‘If it’s this tough against the lower teams, what will it be like against the best?’ Remember we had already lost the first game of the season away at Everton. (Marouane) Fellaini, another huge player, was in the same role as me. He scored, I didn’t.”

Kagawa would start six of United's opening seven matches of the new season, netting twice and assisting once, while he'd also set up two crucial goals in his first two Champions League outings.

It was in the second, a 3-2 home win over Braga, where he would suffer a nasty knee injury that would keep him sidelined for two months and halt the early progress he had been making in Manchester.

The Japan international watched on as United gained momentum over the festive period and began to show real signs of their impending Premier League title victory with crucial wins over Arsenal, Chelsea and City.

Kagawa feared his place in the team was gone, but Ferguson stayed true to his word and eyed the creative talent as a key figure if they were to go on and regain the English top-flight crown.

After overcoming injury the midfielder was back in the starting line-up and was impressing his legendary manager with his professional approach in training.

“The thing that’s quite impressed me is that every exercise we do on the training ground, he’s never needed it to be explained," Ferguson explained.

“After one demonstration, he joins in as if he’s known the language forever. Of course, we know he doesn’t speak the language, but it isn’t a problem.

Sir Alex Ferguson admired the professionalism of Shinji Kagawa

“It just goes to show that a good footballer can pick up exactly what’s needed. He’s been fantastic in that respect. I’ve been surprised at that.”

His crowning moment in a United shirt would come at the beginning of March when Kagawa became the first Asian player to net a Premier League hat-trick thanks to his three calmly taken goals against Norwich.

His role in a 4-0 win would open up an incredible 15-point lead on rivals City as the Japan international brought serenity to a raucous United attack.

As the Premier League trophy drew closer Kagawa would continue to rack up the minutes for United, playing the entirety of their title-clinching 3-0 win against Aston Villa.

This time it was Van Persie who would grab the hat-trick as Ferguson fulfilled his promise of winning the title with Kagawa a central figure of that side.

It seemed like the start of something special, but just two weeks later United's long-serving and brilliant manager announced his shock retirement plans as the title parade soon transformed into a farewell tour.

Kagawa would start and score for United in Ferguson's frantic finale match, a 5-5 draw away at West Brom, as he watched his mentor leave after only one season together.

Just like Van Persie he was left shocked at the manager's exit having been sold the dream of long-term success only a year previous and would suffer as a result under the regime of David Moyes.

“It was his decision, he told us to our face and I respected it,” says Kagawa. “Genuinely. I was a little sad because he had worked for so many years. I wanted to work with him for more years, but everyone has to stop sometimes.”

Even after such a solid debut season in English football there was a real belief United hadn't seen anything close to the best of Kagawa, a thought echoed by mentor Klopp.

Shinji Kagawa won the Premier League in his first season at United

In their first season without their Japanese talisman, Dortmund had reached the Champions League final against Bayern at Wembley, as the German coach used his chance to speak with English media as a plea for United to utilise Kagawa properly.

“Shinji Kagawa is one of the best players in the world and he now plays 20 minutes at Manchester United on the left wing,” said Klopp.

“My heart breaks. Really, I have tears in my eyes. Central midfield is Shinji’s best role. He’s an offensive midfielder with one of the best noses for goal I ever saw. But for most Japanese people it means more to play for Man United than Dortmund.”

If Klopp was in tears after Kagawa's first season at Old Trafford he'd soon be inconsolable when Ferguson was replaced by Moyes.

The former Everton manager had inherited a side in transition but his case was not helped by his own approach which saw hardworking players favoured over the raw attacking talents which he had at his disposal.

As a result Kagawa ended up playing most of his football from out wide and not in the No.10 role he had shone in so brightly at Dortmund, though his case for starting there was not helped by the fact dressing room leader Wayne Rooney now also preferred to play there.

“Rooney was so good that he gave confidence to those around him," the Japanese star added. "He was played as a No.10, usually. Rooney scored, he set up goals. He could dribble, he was even good defensively. He worked so hard. He was the best player I saw in England – and he was in my position. He played in different positions and that didn’t make it easier for me because one of them was mine.”

At the time Kagawa refused to blame Moyes for his inconsistent involvement and insisted it was his own duty 'to improve more and more' if he was to have any hope of surviving at the club.

Kagawa would only start six of United's opening 18 league matches the following season and was taken off at half-time in two of those, only appearing in 10 of the first 30 league fixtures at all.

“I still haven't scored any goals this season so I've felt very irritated," he admitted as frustration slowly overcame an otherwise calm persona.

Shinji Kagawa rarely played under David Moyes

“Actually, if I can't it really shows that I haven't grown as a player. So because of that I have to really focus on the second half of the season and overcome that mental block.”

Kagawa targeted a new physical training regime in order to adapt to the pressures of Premier League life and admitted he needed to be 'stronger' if he was going to remain in the Premier League for the long term.

Such a positive attitude would earn Kagawa a recall under Moyes for his final run of matches in charge, but it was clear the Japanese star had fallen behind January signing Juan Mata and academy sensation Adnan Januzaj in the pecking order.

The Scot's sacking would once again cast doubt over Kagawa's future at the club, but under caretaker boss Ryan Giggs he shone; grabbing an assist in his first match in charge against Norwich and starting three of the final four matches overseen by the Welshman.

The late revival filled him with optimism heading into the new season under manager Louis van Gaal and Kagawa once again made clear his desire to be a key part of more success at United.

"I feel incredibly excited," he exclaimed after the appointment. "It’s a new start and I feel re-energised. It’s up to the players to get the results we need. I have a strong desire to do well.

"I’ll look more closely at my game and accept the challenge filled with passion."

His summer didn't get off to a good start after a disappointing showing at the World Cup in Brazil with Japan, and quickly Kagawa was to learn that he was not a first-choice under his new club manager.

"I was now in my fourth manager in just over two years. I joined a club with the same manager for 25 years and then they had Moyes, Giggs and Van Gaal.

"I felt I needed a new challenge to help me get back to my best. Maybe that could have been in Manchester, but then Angel Di Maria and Radamel Falcao arrived. That only made my situation worse. I knew it was time for me to leave Manchester after two years when Van Gaal said to me: ‘Shinji, you are not going to play as much for me.’

Louis van Gaal did not see a future for Shinji Kagawa at United

“When I heard that – when a player hears that – they think ‘it’s time for me to go.’”

With news of his availability making headlines, it wasn't long before Klopp got in contact to offer his prodigal son another shot at success with him back in Dortmund.

For the Japanese star it was an easy decision to make having only agreed to leave Germany in the first place for the promise of regular football.

"My decision was clear, I wanted to return to BVB and only to BVB," he emphatically stated after a £6.5million fee was agreed between the two clubs. "I want to achieve success with this club again, and with no other.

"Only facts matter in football, stats, goals, assists, titles, and a lot was missing in this regard.

"That was probably why they no longer included me in their plans. Everybody knows that my second year at Manchester United was particularly difficult.

"The manager did not really count on me, and the team was also on a bad run. That means I am all the more delighted to be back. My heart had remained at BVB anyway."

After only two years in Manchester, it would be easy to write off any transfer as a 'flop' but for those who watched Kagawa, such harsh words would never be the case.

In glimpses he showcased the brilliance which saw him adored by both Klopp and Ferguson, though such admiration was not matched by Moyes and Van Gaal.

His continued success upon returning to Dortmund was a testament to his extraordinary ability as the shy shadow striker once again rose to stardom with stellar showings on the pitch under a coach who adored him.

Shinji Kagawa remained hugely popular at Borussia Dortmund

"Shinji is back in the environment in which he feels right," the retired Ferguson reflected on his eventual exit from the club. "He has with Klopp a coach who gives him the necessary self-confidence.

"I was very pleased with Shinji. He had settled in well with me, and I also had the feeling that he felt comfortable with us.

"Every coach has his own philosophy. As Moyes preferred Mata, Kagawa has felt that he is no longer first choice and was a bit resigned."

Kagawa was a player who let his feet do the talking, it is a shame he was silenced for so long.