Moriyasu, who has led Japan since 2018, will remain in charge until the continental championship concludes in February, with Oiwa set to take over as head coach as Japan begin preparations for the 2030 World Cup.
The 57-year-old said his focus was firmly on delivering Asia's biggest prize before stepping aside.
"Whether it is four years, two years, one year or six months, my mindset remains the same towards the goal... that Japan will win the World Cup by 2050," Moriyasu told reporters on Friday.
"I want to bring together the past, the present and the future, while making the best choices for the team today.
"It's a difficult balance, but I intend to select players and build a squad (for the AFC Asian Cup) with a focus on winning the tournament, based on the belief that doing so will help Japanese football continue to grow."
Moriyasu guided Japan to the last 32 at the World Cup before a stoppage-time 2-1 defeat by Brazil ended their campaign last month.
He also led Japan to the Asian Cup final in 2019, where they lost to Qatar. At the 2023 edition, the four-time champions were knocked out in the quarter-finals by Iran.
Japan begin their Group F campaign against Indonesia on January 11th, and Moriyasu said he will be working closely with Oiwa as he aims to build the senior side with an objective of lifting the trophy.
"We have already brought players from the U-21 team led by coach (Go) Oiwa into the senior national team, before returning them to his side," Moriyasu said.
"We will continue to communicate closely, but ultimately the decisions (during the AFC Asian Cup) will be mine, and I'll take full responsibility for managing the team during my time in charge."