>>5958466It's sad because it was literally a true story, and it has one of the worst endings possible. Coco was an outsider who wanted to join into an idol group where she didn't quite fit in because it looked fun. She learned their idol ways, and offered them her unique talents, becoming a core member of the community loved by all despite her differences. Or because of her differences, even. And everyone was happy. For a time.
And then the group changed around her, essentially due to corporate greed, into a place where her unique traits no longer felt welcome. She had the choice of either pretending to be something she isn't, or be true to herself and move on. So she departs.
Also it's a parody of a Little Mermaid song, and her story is basically the opposite of that story. It's like if Ariel married the prince, and then they lived happily for like a year and a half, then Ariel gets hit by a car, and Eric's insurance doesn't cover the cost of the hospital stay and recovery and the financial burden causes him to resent her so they divorce, then Ariel just goes back to the ocean.