"After the short program, I was quite depressed. I was so deeply depressed," he said. "But the fans and the team believed in me."
The silver went to countryman Shoma Uno with a 319.31-point total on a strong day for figure skating in Japan, which has won six of the 12 world championships men's medals awarded over the last four seasons.
China's Jin Boyang was the bronze medalist for the second straight year, scoring 303.58.
"I just want to focus on my program and make it perfect, and I did it," Jin said. "Whether I got a medal or not, I was quite happy."
Three-time world champion Patrick Chan was fifth, while U.S. champion Nathan Chen, a Salt Lake City native, finished sixth after attempting a record six quad jumps in his free skate, with mixed results.
The 17-year-old Chen previously complained of problems with his boots: "Whatever happened, happened, and I just have to put it behind me."
Sixth place for Chen and seventh for Jason Brown meant the U.S. joined Japan as the only two countries to earn the maximum three spots in the men's event at the Olympics.
Saturday's free skate illustrated the relentless march in men's figure skating toward ever more quad jumps, which demand huge power and control from a skater.
The final six skaters to take the ice attempted 24 high-risk quad jumps between them, with three falls and a few more awkward landings.
Also, Canada's Tessa Virtue and Scott Moir survived a slip by Moir on their free dance to win the ice dance, completing a triumphant comeback season.
After spending two years away from competitive skating, the 2010 Olympic gold medalists went a full season unbeaten for the first time.
"We've never had a quote-unquote perfect season, never had that kind of run of golds, and at this point it's fun to have on our resume," Virtue said. "But more than that, what we've been able to accomplish personally as athletes has been the most satisfying."
Papadakis and Cizeron took second with 196.04 after breaking their own record in the free dance with 119.15.
The United States won its only medal of the worlds as siblings Maia and Alex Shibutani took bronze with 185.18.