What the hell went wrong?
The first red-flag was ageing up Raphtalia so she could be a 'proper' heroine. Despite that, it reached a high point when Naofumi smiles after finally finding someone who believes him. However, shortly after, the author jumped the shark by turning the bird into a loli... and to make matters worse, he gave the shield some edgy offensive powers instead of expanding on its defensive capabilities.
And let's just not even mention the god-awful villains.