Zventa Sventana is an ethno fusion band from Moscow; most of their beauty is the aural conflict between two female voices, those of Alyona Romanova and Tina Kuznetsova. Normally, it's a jazz rock fusion band with funky slapping electric bass, electric guitar etc. But this exact video eliminates all pop elements by narrowing the conflict down to the coexistence of two basic elements of which Zventa Sventana's music consists: Russian folk song (represented by Alyona, who is, after all, an ethnomusicologist specializing in Russian music folklore) and the blues (represented by Tina, who is a professional jazz singer.) What Alyona is singing here is stradaniya, a specific type of Russian folk song similar to the blues in its mood -- only, strictly female (never sung by male singers.) I'm sure you'll figure out what Tina is singing.
Oh, yes, and I'm sure everybody recognizes the instrument Alyona is playing: it's a balalaika.