I had a theory about Gumis song, COPYCAT, for a while, and I thought of sharing it.
In the past, she never knew who she was, so every time she meets someone, she will tend to act like them, giving her the name of COPYCAT. She then meets this new person, and tends to do the same. They question it but don't leave her. She then meets other people while meeting this same person, and tends to act like all of them at once.
The line "I'll become what you like, this is what you wanted, right?" I think means that she met someone in her past, who probably said something about getting a personality, and so she remembers this, and says this to herself when she becomes all these people.