Niu

The word "niu" is similar to "no" and

That word makes "no" sound nicer, which is good.

In short, it's a cute refusal or simply a cute answer.

-will you be jealous if I'll come back early in the morning?
-niu, I won't

Dwa

That word is like the word "yes", having the same meaning, except because of that "W", it makes that "yes" cuter and also better.

-Do you love me, baby?
-dwa, I love you!