Fate painted each person's life, some sail through with both parents, kind elders, and all the world's beauty laid out before them. They stand at the crossroads of innumerable paths, each one bathed in golden light, each leading to the promised land. Conversely, others don't have this life; their elders pass away, they lose both parents, all of the world's beauty is irrelevant to them. Their path is thorny, and each step requires hardships unknown to outsiders.
There are many reasons why such disparity exists. Malin's previous life was exceedingly difficult; the world was so painful. The only thing that kept him going was that phrase.
"We must grow old together, right?"
Yes, definitely. Even if I'm the only one to turn grey, I'll still have fulfilled our promise.
Later, in this world, Malin still lived for others, for Maya, for Faye, for Clovis... for every girl who trusted and helped him.