The question of identity ("Who am I?") is important to all the characters in The God of Small Things, but especially to Estha and Rahel. On one level, they have a very good idea of who they are: they are extensions of one another. When they are together, they are a whole being. Nevertheless, the more Estha and Rahel learn about the world around them, the more we see them taking on alternate identities and imagining themselves as someone else. Ambassador E. Pelvis, Ambassador Stick Insect, and The Airport Fairy are all versions of themselves they identify with in different situations. Part of what makes their reunion in 1993 so important is that for the first time in 23 years they can consider themselves whole again.
As kids, Estha and Rahel share one identity.
As kids, Estha and Rahel each have a separate identity that balances the other out.