The 19-year-old stunned the world with his winning march through the men's singles, reaching the final after beating Chinese world number one Shi Yuqi and Paris Olympics bronze medallist Lee Zii Jia of Malaysia.
Lanier, ranked 29th in the world, said he played the best badminton of his career and pledged to "achieve something really huge" at the World Championship in Paris next year.
"I have no words actually," he said of his victory at Yokohama Arena.
"I want to be one of the best players."
The Frenchman, who did not play in the Paris Games, credited his success to hard work over the summer to prepare for the Japan Open.
"I need to win these kinds of tournaments to be prepared for the World Championship, and I will try to do my best in front of the French crowd also," he said
"I'm just now focused on what I'm doing on court, how to play matches against the best ones in the world."
Home favourite and former world champion Akane Yamaguchi cruised to a 21-11, 21-10 victory over Thai challenger Busanan Ongbamrungphan in the women's singles, regaining the crown for the fourth time in a 43-minute showdown.
"Overall, I was able to stay proactive. I was in control of the game throughout. I remained very positive throughout the match and wanted to perform better and better," she said.
The cheers of the home fans also lifted her, Yamaguchi said.
"It was very fun. I was able to stay relaxed. And the results followed," she said.
In the men's doubles final, Goh Sze Fei and Nur Izzuddin of Malaysia beat Kang Min Hyuk and Seo Seung Jae of South Korea 21-19, 21-15.
China's Liu Sheng Shu and Tan Ning beat Baek Ha Na and Lee So Hee of South Korea 21-18, 22-20 in the women's doubles.
The mixed doubles title went to Jiang Zhen Bang and Wei Ya Xin of China, who beat Taiwan's Tang Chun Man and Tse Ying Suet 21-12, 21-12.
