Rainbow Natasha

In 1932, the shadow of war threatens, but Japan is still at peace. A sponsor of the Imperial Symphony, Lord Kuretake Kimiya, is deathly ill. He calls to his bedside Sanjou Kaoru, who is both the fiancé of his daughter Umeko and an up-and-coming conductor. Lord Kuretake has a very serious request: Many years ago, he had a daughter with a Russian woman and he begs Sanjou to search for her in Shanghai. Because her mother, Anastasia, an opera singer, was a close friend of the princess, when the revolution came, she vanished with the imperial family. Since then, Kuretake has married and had a family, and he wants his daughter Natasha to be raised in his home.

Secretly, Sanjou and his manager Nagaoka travel to Shanghai and Sanjou meets a beautiful girl singing at a jazz club in a hotel. Because she’s scorned for her mixed race, she has become a rough tomboy… and it turns out that girl is Natasha! She has been raised by the Kurisaki family, who own a small restaurant, and she and their son Takeshi are like brother and sister. Sanjou invites Natasha to a concert, but at the last minute she must stand in for the star. Sanjou is amazed by her incredible singing voice. Now he determines not only to bring her home, but to make sure she gets proper opera training and becomes a true prima donna. Even Takeshi tells her it would be best to go to Japan. Takeshi, it turns out, thinks of Natasha as more than a sister. Not wanting to risk never seeing Sanjou again, Natasha goes on the boat with him to Japan.

But life in Japan proves to be nothing but misery for Natasha. The Kuretake family treats her like a servant and Umeko is suspicious of her relationship with Sanjou. As she travels home from school, Natasha learns that Lord Kuretake has died. She decides to run away. Takeshi has followed her to Japan, and he and Sanjou search desperately for her on the city streets…

source: https://www.mangaupdates.com/series/wr2mazv/niji-no-natasha