Coach says Japan must improve in 'many aspects' after Asian Cup exit
Japan were runners-up in 2019 and the four-time champions came into the tournament in Qatar as favourites.
But they were never really convincing during the competition and went out in a dramatic defeat to Iran with a stoppage-time penalty.
"I feel sorry for our supporters and everyone involved in Japanese football," said Moriyasu, who took Japan to the knockout rounds of the 2022 World Cup.
He said that he also "regretted" that his team were not able to bring "a happier moment" to victims of a recent earthquake in Japan.
"I also feel responsible for the result," added Moriyasu, who is likely to face criticism back home for failing to take his team further.
"My staff and my players gave everything," he said.
"They prepared as much as they could towards this game and this tournament."
Despite that Moriyasu, who has been Japan coach since 2018, said his side "need to improve in many aspects".
"We conceded at least one goal in every match at the tournament.
"If you can't keep a clean sheet you can't win. We suffered a lot today in open play and set pieces."
Iran will face hosts and holders Qatar or Uzbekistan in the semi-finals.