An interesting introduction to Godel's Incompleteness Theorems. Starting with number theory, set theory, formal systems, and logic, the book slowly builds up the knowledge required to understand Godel's proof. It tries to avoid metaphysics and philosophical discussions by having its characters constantly dissuade each other from trying to make grandiose statements about mathematics being "incomplete", sticking mostly to an explanation of Godel's proof.
For those looking for some development to the actual Math Girls "story", there is a hint about where the main character ends up in a short epilogue, but there's more math than story. Perhaps the manga covers that in greater detail.