"Flags of Our Fathers," telling the U.S. perspective of the battle, and the tentatively titled "Lamps Before the Wind," telling the Japanese side, will be released simultaneously, Time magazine reports.
Eastwood is scheduled to start shooting "Lamps" in February, Time says in the issue on stands Monday.
"Million Dollar Baby" writer Paul Haggis wrote "Flags" while the companion film was penned by Japanese-American screenwriter Iris Yamashita, Time said.
The two films will focus on the clash of cultures as well as clash of wills between U.S. soldiers and Japan's military, Time said.
Eastwood said the Japanese officers took their men into battle and possible death because it was dishonorable to surrender. The drive behind the U.S. forces was different, he said.
"They knew they were going into harm's way, but you can't tell an American he's absolutely fated to die," Eastwood said. He will work hard to get the job done, but he'll also work hard to stay alive and to protect his comrades in arms."