Miya Shimada was born a nisei — a Japanese-American born in the United States of native Japanese parents. She was thus a full American citizen and grew up in Santa Barbara, California.
The racial prejudice against Japanese-Americans that Miya encountered during the start of World War II caused her to turn against America. She went to Japan to study for a few years and there she joined the cause of the Imperial Japanese government. It was the famed Japanese naval commander Admiral Yamamoto who named Miya Shimada "Tsunami" (the Japanese word for "tidal wave") after her mental power to create and control such waves.
In early 1942, after the United States had entered the war against Japan, Tsunami was secretly brought to California by a Japanese submarine and she sought to convince Japanese-Americans to join Imperial Japan's cause. Tsunami soon found herself battling Liberty Belle and Starman of the All-Star Squadron, and when her father was seemingly killed in the skirmish, Tsunami went berserk but failed to defeat them and departed instead.
Shortly afterwards, Tsunami was summoned by Japan's Prince Daka to assist him in stealing Starman's powerful gravity rod. She again clashed with members of the All-Star Squadron but was appalled by Daka's ruthlessness and lack of honor. She found herself instead respecting the All-Stars and decided she could no longer side with Daka. Yet she was not yet ready to align with the Americans either, and she fled again.
One more time, the Axis powers attempted to recruit Tsunami, but by this time she had reflected upon and felt remorse for her actions. She declined an invitation by the German villain Sea Wolf to join the Axis Amerika and afterwards became depressed and contemplated suicide. At a critial moment, she met another undersea hero, Neptune Perkins, who convinced her to try another path.  Together they approached Green Lantern for his help to end the imprisonment of Japanese Americans.
Green Lantern took the two to meet the Squadron. Miya pled her case to the day's assembly, which also included President Roosevelt. FDR pleged to look into the matter of the detention camps then suggested that Tsunami and her new young friends travel the country on a cross-country war bond tour. She and the others were all given provisional membership in the All-Star Squadron and set off.
Some, like Sandy found it difficult to accept a former adversary, but Perkins was always ready to defend her. On one of their first stops, Miya came under attack by prejudiced bystanders in Los Angeles. The group helped her find her family in a nearby camp, where she elected to stay until they could be freed.  She was soon forced to leave the camp when she learned that Axis Amerika and her former ally, Kamikaze, had attacked.
Naturally, Miya grew close to Neptune Perkins during this time, after the war they raised a daughter named Debbie Perkins (Deep Blue), who was actually fathered by Atlan and therefore is Aquaman's half sister.
- Hydrokinesis: Tsunami can mentally cause and control tidal waves.
- Superhuman Strength
- Superhuman Speed
- Although this character was originally introduced during DC's Earth-Two era of publication, their existence following the events of the 1985-86 limited series Crisis on Infinite Earths remains intact. However, some elements of the character's Pre-Crisis history may have been altered or removed for Post-Crisis New Earth continuity, and no longer apply.
- 48 Appearances of Miya Shimada (New Earth)
- 11 Images featuring Miya Shimada (New Earth)
- Quotations by or about Miya Shimada (New Earth)
- Character Gallery: Miya Shimada (New Earth)