This is something that’s been bugging me for a while. We normally think of Russians as white people, and Chinese as Asians, right? So what about the folks on the border between the two countries? Is there a sharp dividing line between ethnic groups, or is it more of a gradual transition?
There’s always a gradual transition between ethnic groups.
Generally, Asians in that part of the world look, well, Asian. But keep in mind that many Europeans from western Russia have migrated to eastern parts of Russia over the years, but the indiginous people look more Asian than European, especially since the Sino/Russian border is waaaaaaay to the east of the Ural Mountains (the traditional border between Europe and Asia, at least geographically). In fact. it’s east of Mongolia.
Siberia was ethnically Asiatic many thousands of years before any Russians showed their pasty white faces there. The Altai Mountain region on the borders of Russia, Kazakhstan, Mongolia, and China is thought by Turkologists to have been the ancestral homeland Urheimat of the Proto-Turks. Today the ethnic groups along the border area include Altay Turks, Tuvans (speaking a Turkic language, ethnically of mixed Mongol-Turkish origin), Mongols (Khalkha and Buryat), Uyghur Turks, and Kazakh Turks in the west. Along the eastern portion of the Russia-China border are Tungusic-speaking peoples like the Manchu and Evenki. Turkic, Mongolic, and Tungus-Manchu are the three branches of the Altaic language family, whose existence is a bit controversial. Whether or not the three groups are organically related, they share many linguistic features in common.
Practitioners of the famous Tuvan throat singing. Now that’s an art!
For the OP, fyi, here’s a picture of some Tuvans. And they’re still pretty far west of the eastern most parts of Russia.
Use google image for “Heihe City”
It should also be noted that “Russia, the home territory of the Russian people” is not ethnically coterminous with “Russia, the extents of the Czarist Empire and Soviet Union”. There’s a lot of eastern Russia that has no ties other than political with the ethnic Russians.
I’d also like to point out that while ethnic Russias are typically considered white/Caucasian Europeans, if you really look at them you’ll see a certain amount of Asian influence in many of them, including but not limited to high checkbones and epicanthal folds. There are other Asiatic features occuring among ethnic Russians at higher rates than, say, Poles or Czechs, but they probably are not as well known or obvious to the average person.
Actually, I wonder if the OP might be wondering how a lost Japanese man from WWII could be living in Russia all these years…and no one notices? 
Except that he’s been in Ukraine for most of that time.
An “asian looking” person would not be completely out of place in Russia, but someone who spoke Japanese as his first language sure would be.
As a result of 20th-century wars and population shifts, there were ethnic Koreans and Vietnamese settled in various parts of the Soviet Union, and are probably still there. For 1,000 years, from the 5th century until the 15th, the way was open for Turks to cross the steppes and settle in Russia.
What is now the Volga-Kama area of eastern Russia, centered on Tatarstan, had been a Turkic-speaking area from around the 5th century AD. The original Altaic people on the Volga were called the Bulgar. They came across the steppes from Central Asia then perhaps as part of the movements of peoples associated with the Hun invasion of Europe. A branch of Bulgars went south and fought the Byzantine Empire; they gave their name to the country north of Greece, but were later replaced ethnically by the Slavic influx.
The Volga Bulgars spoke a strongly divergent branch of Turkic known as “r-Turkic” for its sound shifts. It has /r/ where other Turkic languages have /z/. The early Magyars on the steppes of southern Russia associated with Turkic tribes who shared their nomadic life, and this is how the Hungarian language got its r-Turkic loanwords. For example, ‘write’ is yaz in Turkish and ír in Hungarian, a contraction of a Bulgar word that must have been *yar or something like that. Today the only surviving r-Turkish language is Chuvash, spoken in a republic of Russia adjacent to Tatarstan. Some linguists think Chuvash is a separate branch of Altaic, more closely related to Mongolian than Turkish in some respects. The Khazars who dominated the lower Volga in the 9th century apparently spoke another branch of Turkic.
The Mongol conquest in the 13th century brought in the Tatars who settled along the Volga. The Mongols faded out within a century after their conquest, but the Tatars stayed and founded the Kazan’ Khanate, which was conquered by Ivan the Terrible in Russia’s first big territorial expansion. The Tatars speak a language from the Qypchaq branch of Turkic, which also includes Bashkir, Kazakh, and Kyrgyz. They’re still there and have declared independence from Russia (on paper only).
Then we can’t forget those people with the wild dances composed by Alexander Borodin whom the Russians called Polovtsi, whose real name was Cuman. They too spoke a Qypchaq language. Descendants of the fierce Pechenegs who fought the Byzantines, the Cumans were pushed out of Russia by the Mongol invasion and went to Hungary, where they became temporarily influential and the bad boy of the Hungarian monarchy, László IV, was half Cuman.
So all of this shows that much of what is now Russia was Turkic in centuries past, and was Russified only in the past half century. No wonder Asiatic features show up in so many Russian faces. There’s a proverb, “Scratch a Russian, find a Tatar.”