It's a metal box that wouldn't look out of place in Heart Soldier's dorm. There's a huge padlock closing it shut.

When you pick it up, you can get an impression of its contents. What's inside is -

Disillusionment (you shouldn't have put faith in them); anger (why did you have to pay for their actions?); regret (maybe you should have just said nothing); guilt (you aren't kind or gentle); inadequacy (you are not and never will be noble of heart); loss (you never belonged) -

Probably, there are many reasons this box should stay locked.