The 19-year-old, born in Nishitokyo in 2006, has signed a contract running until 2031 and becomes Valencia's third summer signing, following the earlier arrival of Justin De Haas and Guido Rodriguez's permanent deal. He will wear the number 39 shirt, having come through the FC Tokyo academy, where he made his first-team debut aged just 16 in 2023.
A loan at Fagiano Okayama in 2025 proved decisive in his development, with Sato earning the J1 League's Best Young Player award and a fan-voted place in the division's All-Star selection before returning to Tokyo, where he scored six goals in 19 appearances ahead of his move to Spain.
Real Sociedad's Take Kubo welcomed his compatriot to Spanish football with a short video message in Japanese.
"I hope we meet on the pitch," Kubo said. The press conference was conducted in Japanese with consecutive translation, with Sato committing to learn Spanish as quickly as possible.
Asked what it meant to represent Japan in Europe, Sato said: "I already knew before coming here that this club is very important in Spain. And I notice and feel it more every day, and I'm very happy to be part of this club."
On his decision to join Valencia specifically, he added: "I wanted to come to Valencia, it was my wish. I didn't hesitate for a single moment. It's my personal challenge to grow here at this club."
Sato praised the standard of Spanish football.
"LaLiga is the best competition in the world, both for the level of play and for the atmosphere of the fans," he said. "I see Valencia as a team that plays very fast, and I'd like to contribute my grain of sand."
He revealed his shirt number carried personal significance: "It was my favourite number at Fagiano Okayama, that's why I like it," he said of the number 39.
Sato also spoke of the influence of countryman Shinji Kagawa on his career.
"He was my idol growing up, my target to chase," he said. "I've spoken to him, he congratulated me and encouraged me a lot. Unfortunately I haven't been able to speak to Kubo yet."
On breaking new ground for Japanese football at Valencia, Sato said: "Being the first Japanese player at Valencia is a source of pride. What I want is to play well, be part of my team, and be recognised as one of the group."
Asked whether he had the character to match Kubo's numbers in LaLiga, he added: "They say the league is a little difficult for Japanese players, but it doesn't matter that I'm Japanese. The important thing is to work hard and adapt well. Kubo is getting great results and is the path to follow — I'd like to be like him."