well, for the record, I'm pretty sure if you get bad grades you can still feel depressed or have low self esteem, regardless of where you live, not just japan.
For making your characters relatable, then there's a six letter word that serves as a pretty good shortcut.
Faults
Give a character a good fault, and it humanizes them, makes them more real. like the others said, the character doesn't have to be a surrogate for the reader, they just have to be relatable, ie human. humans are full of faults of one form or another. everybody has em. if you make a character perfect, then there's nothing human about them to latch onto.
of course don't go too far with it. choose character faults wisely, and don't bring them up too often. too much and it starts to feel like your playing the pity card, or worse, a character's faults come to define them. you could go for that sometimes, but make sure it's on purpose.