The Betrayed Swordsman
Y/N Briggs was very popular at Beacon. He was kind and courteous to everyone. Even team CRDL treated him with respect. However, while on a mission with his team, he is stabbed in the back (metaphorically) and left for dead by someone he once trusted. Before he fades away, however, a strange old man rescues him from the brink, and worked tirelessly to revive and rehabilitate the wounded Huntsman in training, but he isn't able to save every part of him.
After two months of contact being lost, everyone thinks Y/N is dead, and no one is more devastated than his friends in JNPR and RWBY and two of his teammates, who's grief alone would be able to attract massive numbers of Grimm.
Then one day, Y/N comes back. But he's different. On top of being even stronger than he was before, his personality had reversed. Where he was once warm and friendly, now he is bitter and distant. Where he was once a boundless source of happiness, he has been reduced to cynicism and anger, and it's unclear if he will ever be able to heal.