Moriyasu, Japan's longest-serving coach, was originally set to lead the team at the Asian Cup in Saudi Arabia in January before handing the reins to current Under-23 boss Go Oiwa.
Coach Hajime Moriyasu said Japan can become the best in the world after beating Brazil for a second time, as he prepares to step down after eight years in charge.
Japan shocked the five-times world champions 3-2 in a friendly in Singapore on Saturday, with substitute Tatsuhiro Sakamoto scoring an injury-time winner.
The victory came just more than a year after Japan beat Brazil for the first time in a friendly in Tokyo.
Brazil eliminated Japan from this year's World Cup in North America with a 2-1 win in the last 32.
Moriyasu will leave his job after a friendly against Paraguay on Tuesday but he is certain that Japan are on track to become a major football nation.
"The players showed confidence and courage and dug in when they needed to dig in," he said.
"At the World Cup in the future, Japan can absolutely become the world's best."
Moriyasu, Japan's longest-serving coach, was originally set to lead the team at the Asian Cup in Saudi Arabia in January before handing the reins to current Under-23 boss Go Oiwa.
