Luka Megurine is a VIRTUAL SINGER who watches over the various SEKAIs: School, Stage, Street, Wonderland, and Empty. In all SEKAIs (except Empty), Luka takes on the personality of a cool, mature, and loving young woman that often serves as a mentor figure. In the Street SEKAI, Luka is a carefree girl who does whatever she pleases, and in the Wonderland SEKAI Luka is constantly sleepy. In the Empty SEKAI, Luka is cold, closed-off, and blunt, but protective. 

Voice: Luka has a cool, delicate, and mature voice, that differs slightly depending on which SEKAI she is in.

Reference: https://youtu.be/lHsLKUW0VZI