Question: Why weren't the soviets mentioned by Hirohito?
About the article "Atomic bombings of Hiroshima and Nagasaki", section "Surrender of Japan and subsequent occupation".

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The name Hirohito can refer to:  Hirohito, Emperor Shōwa of Japan; reigned 1926 to 1989  Hirohito Furui, a Japanese keyboardist, music arranger, and musician  Hirohito Gotō, a Japanese director, playwright, and actor  Hirohito Ōta, a Japanese freelance writer  Hirohito Takiguchi, a Japanese social activist  
Hirohito and the Making of Modern Japan (2000, ISBN 978-0-06-019314-0) is a book by Herbert P. Bix covering the reign of Emperor Hirohito of Japan from 1926 until his death in 1989.
It won the 2001 Pulitzer Prize for General Non-Fiction. 
Naoru Tanaka, a chamberlain of Japan for Hirohito remembered an episode which took place in September 1965, on the day Hirohito returned from a 2-month stay from his summer resort.
On the previous day, Tanaka had ordered the cleaning of the very thick weed and bush of garden of Hirohito.
Hirohito scolded him asking why he ordered the cleaning.
He replied that the weed was so thick.
Hirohito said that there was no such word as weed.
Every plant had its name.
Since then, every question of Hirohito concerning plants came to him, although his speciality was geography.
Hirohito loved nature, but thought of birds coming to the Palace and he ordered plants for wild birds be planted, such as Piracantha, idesia, ardisia japonica, Ilex rotunda, Ilex serrata and Viburnum plicatum var.
tomentosum.
According to Tanaka, Hirohito's idea of leaving old-Tokyo woods in the Palace was based on his experience of the great Earthquake of Kanto area of 1923; it should be a place for evacuation. 
 Chinese Sovereign Imperial cult (ancient Rome) Japanese Emperor (The term appears in the World War II American propaganda film "Why We Fight" to describe Japanese Emperor Hirohito.)
Pharaoh Sapa Inca  
Until August 9, Japan's war council still insisted on its four conditions for surrender.
On that day Hirohito ordered Kōichi Kido to "quickly control the situation ... because the Soviet Union has declared war against us."
He then held an Imperial conference during which he authorized minister Shigenori Tōgō to notify the Allies that Japan would accept their terms on one condition, that the declaration "does not comprise any demand which prejudices the prerogatives of His Majesty as a Sovereign ruler.
"On August 12, the Emperor informed the imperial family of his decision to surrender.
One of his uncles, Prince Asaka, then asked whether the war would be continued if the "kokutai" could not be preserved.
Hirohito simply replied "Of course."
As the Allied terms seemed to leave intact the principle of the preservation of the Throne, Hirohito recorded on August 14 his capitulation announcement which was broadcast to the Japanese nation the next day despite a short rebellion by militarists opposed to the surrender.
In his declaration, Hirohito referred to the atomic bombings:In his "Rescript to the Soldiers and Sailors" delivered on August 17, he stressed the impact of the Soviet invasion and his decision to surrender, omitting any mention of the bombs.
Hirohito met with General MacArthur on September 27, saying to him that "he peace party did not prevail until the bombing of Hiroshima created a situation which could be dramatized."
Furthermore, the "Rescript to the Soldiers and Sailors" speech he told MacArthur about was just personal, not political, and never stated that the Soviet intervention in Manchuria was the main reason for surrender.
In fact, a day after the bombing of Nagasaki and the Soviet invasion of Manchuria, Hirohito ordered his advisers, primarily Chief Cabinet Secretary Hisatsune Sakomizu, Kawada Mizuho, and Masahiro Yasuoka, to write up a surrender speech.
In Hirohito's speech, days before announcing it on radio on August 15, he gave three major reasons for surrender: Tokyo's defenses would not be complete before the American invasion of Japan, Ise Shrine would be lost to the Americans, and atomic weapons deployed by the Americans would lead to the death of the entire Japanese race.
Despite the Soviet intervention, Hirohito did not mention the Soviets as the main factor for surrender.