There is a reason you can't hear player's sound in the game.

No Voice for Japanese Language

If you open the main menu and click on the Voice you will see two languages, Japanese and Russian.

If you choose Japanese, you will only hear Mita's voice and if you choose Russian, you will hear both player and Mita's voice.

This is because the Japanese language only has voice actress for Mita and not for the Player, and the Russian language has voice actors for both Player and Mita.

Bug

Some people have said that they have no problem in player's voice on any language so This might be just a bug and get fixed in later updates.