Christian Burgess couldn't quite believe what he had just seen. His side, Royale Union Saint-Gilloise, were trailing 2-0 and down to 10 men against RFC Seraing. Rather than try to limit the damage, manager Felice Mazzu made an attacking substitution at half-time that changed everything.

"He just completely took the game by the scruff of the neck and won it for us. It was like the Kaoru Mitoma show. He was unstoppable," says Burgess, an English defender who previously played for Middlesbrough and Portsmouth.

"He got the ball from deep and ran the length of the pitch to score the fourth. I remember thinking 'Wow, that was special'. That was when he announced himself as a seriously capable player."

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Burgess and the rest of his Union team-mates knew little about Mitoma when he first arrived in Belgium. Now they can boast about having seen one of the breakthrough stars of the Premier League season take his first steps in European football up close.

Brighton are famed for the global focus of their shrewd recruitment strategy. Mitoma joined from Kawasaki Frontale in August 2021, but was immediately sent on loan to Union, who are also owned by the Seagulls' chairman Tony Bloom.

"He was very quiet. He was a nice, humble guy but he didn't speak a lot. He was a bit of a shy character," explains Burgess.

"I think he had a good support unit come over with him from Japan. His wife and a physio came over, so he had that support and familiarity at home. He just expressed himself on the pitch."

Burgess remembers laughing as Mitoma repeatedly skipped past Jonas Bager with ease in one of his first training sessions at Union. The Danish centre-back grew so frustrated that he eventually resorted to clearing him out with a tough tackle.

"When he's running at you, and it's one v one, it's hard to know what to do. He can go outside and still get around you with his pace and bring the ball on to his right foot to finish. If you cover that, he'll cut inside and just pass it into the far corner," says Burgess.

"When you do stop him, you feel like a very good player, but it didn't happen as much as I would have liked! It was obvious that he had a lot of ability and could go and play at the top level."

Despite impressing his team-mates in training, Mitoma initially had to bide his time as Union took the top level by storm. Up until that unforgettable performance against Seraing in October, he had only been used as a substitute in the league.

Tiring defences couldn't cope with Mitoma's devastating combination of speed and skill. In 29 appearances, 17 of them starts, there were eight goals, four assists and countless flashes of inspiration.

Christian Burgess (second from left) was impressed by Kaoru Mitoma (third left) at Royale Union

Burgess said: "His change of pace is just scary. When he chops inside, or chops again and goes outside, he's just too quick with his movement and his first few steps of acceleration. It's deadly. I saw him do it to Trent Alexander-Arnold recently and he made it look easy."

Mitoma's ability made him a perfect outlet for Union. If they were struggling, he could relieve pressure and carry his team up the pitch.

"Sometimes, when you're under the cosh, you'd just think 'Okay, if we win the ball back, we'll give it Kaoru and let him do his thing'," said Burgess.

"As soon as he had the ball, other teams would try to double up or they would just drop off because his pace was too much. It gave us all a breather at the back."

Mitoma developed a toughness during his loan spell - the resilience and fighting spirit that would be needed to make an impression on the Premier League.

After Union had finished the regular season in top spot, he raised his game in the play-offs, starting five out of the six matches and scoring in both wins over local rivals Anderlecht.

"He took things maybe a little bit more personally and really wanted to be successful, whereas I think at the start he was just trying to fit in and adapt to his surroundings," said Burgess.

In the end, Union narrowly missed out on the title to Club Bruges and Mitoma went back to Brighton, who had been following his progress closely. Once more an impact substitute in the early stages of the season, he has blossomed into perhaps their most dangerous player under Roberto de Zerbi.

Since returning from the World Cup, where he helped Japan beat Germany and Spain on their way to a spot in the last 16, Mitoma has scored in three of his last four league appearances, including a superb curling finish into the top corner against Leicester City, as the entertaining Seagulls have climbed to sixth. He also struck a stunning winner in the FA Cup fourth-round victory over Liverpool.

A late bloomer who elected to graduate from university before starting his professional career, the 25-year-old winger was in no rush to reach the top.

"You like to see good people, and people who work hard, do well," said Burgess. "If anyone deserves it, it's Kaoru. It's not easy going from Japan to England via Belgium, not speaking the language and not being around your family and friends. He's taken it all in his stride and he's just got better and better. He's reaping some of the rewards and I'm really pleased for him."