Opus

Opus is a manga series by Satoshi Kon.

Plot
Opus is Kon's metafictional tale of Chikara Nagai, a creator under pressure to finish his latest graphic novel, Resonance, who finds that the harshest critic of the shock ending he's got planned is the character who'll have to die in it! Nagai's strengths and weaknesses as a creator are tested beyond their limits as his present and his past, and the worlds of the manga and of reality, become the levels of a maze he may never escape... let alone get a chance to resolve the story!