The series has the names 'Yuuko' and 'Okonogi'. If you know Dennou Coil, it will remind you of the anime's main heroine, Yuuko Okonogi a.k.a. Yasako. Interestingly enough, there is another 'Yuuko' in Dennou Coil: Yuuko Amasawa a.k.a. Isako.
Talking To Herself: Both Yuuko and Shadow Yuuko are voiced by Yumi Hara, which is obvious since both girls are the same person. However, because Yumi uses a different and scarier voice for Shadow Yuuko, it doesn't sound like her.