Sonic the Hedgehog (Shogakukan)

Nikki has ability to turn into Sonic the Hedgehog, as this incarnation of the main character is Nikki's alternate persona.

Personality
Cocky and overconfident, Sonic seems to be the exact opposite of Nikki. Sonic arrives always just in the nick of time to save the day and he always knows what must be done. Sarcastic and heroic he appears to be perfect. The peculiar thing is he has a conscience and a memory of his own that seems to have nothing to do with Nikki's (explaining Nikki's obliviousness to Sonic's existence).