A new star is born.
The 19-year-old delighted the home crowd at the Nippon Budokan as she defeated 2012 Olympic champion Idalys Ortiz from Cuba in a closely-fought final.
Japan's world number six won her first senior world title on shido penalties four minutes into golden score time when Ortiz was penalised for stepping out of the main blue contest area.
"I prepared really hard and I'm very happy. It was obviously my goal to win gold. I spent the entire day just thinking about winning the championship," Sone told reporters after her win.
"[Ortiz] is so strong but I couldn’t let her beat me mentally. I had to show that I have a strong heart if I was to going to beat her.
"My goal is to make it to the Tokyo Olympics and win a gold medal there, and that is something I definitely hope to achieve." - Akira Sone after becoming +78kg world champion
Disappointment for Asahina
Japan now have the last two world champions in the +78kg class in Sone and Sarah Asahina.
But only one will be able to represent the hosts at Tokyo 2020.
Japan's defending champion was eliminated in the quarter-finals, before taking bronze in the small final.
Three-time world medallist Asahina said afterwards, "I'm from Tokyo and I was excited to perform in front of my people. My aim was to win gold and I am a bit disappointed for this bronze medal. I will re-start from this defeat to improve my skills."
Japan women's coach Katsuyuki Masuchi said,"We didn’t think Asahina would lose the way she did but we still have the team event left and we need to regroup for that."
Kayra Sayit of Turkey repeated her bronze from Baku 2018 after beating Brazil’s Beatriz Souza.
Two titles in two categories
Lukas Krpalek was crowned world champion for the second time in his career.
The 28-year-old Czech added a super-heavyweight gold to his half-heavyweight title from 2014 in Chelyabinsk, Russia.
The -100kg Rio 2016 champion defeated Olympic silver medallist Hisayoshi Harasawa in golden score time after forcing a third shido penalty from the tired Japanese opponent.
"I feel very well, it's an amazing day for me. I did my best and I won", Krpalek told reporters after the final.
"It was my big dream to win the Euro Championships and the world title in two different categories." - Lukas Krpalek
"I hope I can also win the European title in Prague next year and a gold medal next year in the Budokan, where the 1964 Games were held."
Asked how he plans to take Teddy Riner's crown next year, he answered: "Winning a competition without him it's not the same. I hope to face him at the Euro Championships. I want to be the man who's going to beat him."
Harasawa, who went down to Riner in the final of Rio 2016 and the Frenchman's comeback in Montreal in July, admitted, "With Riner not here, my goal was to win a gold medal so this is disappointing to be honest.
"I ran out of stamina in the final. I’ve got a lot to work on across the board."
Kim Min-jong from South Korea celebrated his 19th birthday a day early by claiming bronze against Brazil’s Rafael Silva.
Roy Meyer of the Netherlands beat reigning world and European champion Guram Tushishvili in the second small final.