So what's the plot of the game in the end?

[Delicious Pancakes]

My understanding is that the game itself is a representation of the human condition when he learns that he is about to die.
Between doing nothing and doing something, Ash chose to find a friend, knowing in advance that there was no point and the world was doomed.
I think he was really happy when he finally made a friend. I mean, he was his last goal in life. That's why he let him go so easily.
One last goal accomplished.

[HalvedDead]

edmund has said stuff about the plot, mainly the point of it all was to show that even though you could do big things and achieve your goals, in the end it could only be a little worthwhile, not worth it at all or even detrimental. its up to you to properly evaluate if whether your end goals will truly bring you happiness is what i have taken away from it.