When you're in the bullet hell and growing frustrated, you slowly start to see messages from players all around the world leaving encouraging messages, mostly with things like "don't give up" or "we'll help you!". And then after dying a certain number of times, the game offers you help from these players who did a drastic thing (in deleting all of their save data. All of it, to help out other players in end end). And when you accept it and they join in, the music goes from one single singer, to a chorus of many as you overcome the last bits. It was just a very touching thing to me to see you get annoyed at what seems impossible, and then the game pulls a Persona 3 and friends come to lend you strength.

I found it most interesting because games love to show self sacrifice constantly. It's a very cool thing to see it actually implemented as a mechanic to help a total stranger at the sacrifice of the dozens of hours you've sunk into the game, to help someone you'll never met.

the original Nier did something along the same lines I believe, though it was a bit more drastic since no one would remember you, and you couldn't even use that same username anymore.