"Kazuki has adapted to German football faster than expected. He is fully integrated into the team and put in some good performances in the second-half of the season," explained club boss Joerg Jacob with Cologne back in the Bundesliga after winning the second division title.

"We believe that he still has great potential and we are glad that we can continue to develop him."

The 22-year-old joined Cologne in December and had originally signed a contract until 2016, but after making ten league appearances he has impressed the German club.

"I have felt good at the club and in the city since my first few days here," said Nagasawa, who has yet to make his debut for Japan and has not been included in their World Cup squad.

"I'm looking forward to the challenge of the Bundesliga and I want to continue to be an ambassador for the club in Japan and for the city of Cologne."