To get this you must equip the "Mother Bug" ability for D'Vorah. Go to Kustomize, then characters, click on D'Vorah, then onto any variation, and hit
to get to the Abilities tab. Uncheck anything that is ticked, then equip Mother Bug.
Now go into a local versus, set it to Very Easy, and after selecting D'Vorah ensure you have selected the variation with the ability on. Now whittle down your opponent until they have low health, then let them beat you up. When your health gets to critical levels you will suddenly take control of a bug. As the bug, hit your opponent to take him out. After switching back to D'Vorah finish your opponent to unlock this.
Here is a visual guide courtesy of Maka: