Who was Hajime talking to at the end of Gatchaman Crowds? At the end of the last episode:


  She called her mother to tell her that no matter what happens, "I'm just me". Then after the credits, Hajime was tapping her chest and was having a conversation with someone with another voice. Who was she talking to? Was that supposed to be Katze?
Yes, that's Katze.

Most of the time, Katze talks with a high pitch, especially when bullying people. However, when Katze is not in control of the situation, his/her voice drops. This can be heard several times in the battle between O.D. and Katze that starts at 6:05 in the same episode. It's the same voice.

Besides, at the end of the series everybody else likes Hajime; who except Katze would claim to be sickened by her? :-)