Fresh off an impressive 4-1 thrashing of South Korea, Nielsen's Japanese outfit will lock horns with the Matildas at Sydney's Stadium Australia in Saturday's final.
The Greenlander has overseen a near-faultless campaign in which Japan have been on another level to most of their opponents, netting 28 goals and conceding just one across five-straight wins.
Nielsen has coached Denmark and Switzerland but crossed paths with Australia's defensive midfielder Alanna Kennedy and Fowler during a brief spell as a technical director at Women's Super League giants Manchester City.
He lavished praise on Kennedy, who was overtaken in the golden boot standings by Japan's Riko Ueki after she grabbed her sixth goal of the tournament against the Koreans in Sydney on Wednesday.
But Nielsen conceded Fowler had a special place in his heart.
"Alanna, I know from Man City and I just want the best for her because she's such a great girl," Nielsen said.
"My absolute favourite player in the whole of world football that I ever had anything to do with is Mary Fowler.
"She's just a character from another world and those of you that know her better than I do, you can understand what I mean.
"She's special, so take care of her because you should be very proud to have an Australian player that has a character like that."
Nielsen also said he was a good friend of Australia coach Joe Montemurro and praised him for how he had navigated the absence of Steph Catley, Hayley Raso and Mackenzie Arnold through large parts of the tournament.
And even if the Matildas have not been as dominant as the Japanese, Nielsen knows his side have to be on their game throughout Saturday's final.
"I love the players I know, I even love some of those that I don't know," he said.
"I think it's amazing that Sam Kerr can just keep scoring - she's so dangerous, a top, world-class striker.
"(Caitlin) Foord, the way she has been playing is so dangerous and Ellie Carpenter, is a machine.
"I don't think she can get tired. I'm waiting, maybe she will be a little bit tired in the final, I hope!"
Nielsen knows Japan will be playing in front of a heavily pro-Australian crowd but doesn't want to be depicted as the villains of the final.
"I don't consider us bad guys, I'm never really the bad guy," he said.
"I know a lot of people want the Matildas to win, and I can understand why.
"If I had been from Australia, maybe I would feel like Australia should win as well. But I'm not, and I will be honest with you, I'm hoping that we can beat them."
