YOU SAID:

Senpai, it feels so good! My hips are moving on their own!

INTO JAPANESE

先輩、とてもいい感じです！私の腰は自分で動いている！

BACK INTO ENGLISH

Senior, it is a very nice feeling! My waist is moving by myself!

INTO JAPANESE

シニア、とてもいい気分です！私の腰は自分で動いている！

BACK INTO ENGLISH

Senior, I feel very good! My waist is moving by myself!

INTO JAPANESE

シニア、私はとても良い気分です！私の腰は自分で動いている！

BACK INTO ENGLISH

Senior, I feel very good! My waist is moving by myself!