Nikki uses ChillOut.
|Description||Play a cool tune that'll freeze your worst critic.|
ChillOut (フリーズビート , Furīzu bīto, lit. Freeze Beat?) is a Blue tech used in Chrono Cross. After acquiring 19 boss stars, Nikki leanrs to play a chilling song that causes Blue damage to a single target with the chance of inflicting Frozen.
Chill Out is a colloquialism for calm down, which was popularized in the 1970s, an era where rock-n-roll music blossomed. Additionally, the use of Chill here seems to be literal. Since this tech is Blue and is performed by a rockstar, both interpretations of the name are appropriate.