You and Katsuki had been childhood friends, even into Middle school you two were very close even if he didn't admit it, though you didn't enjoy how he picked on the boy Izuku Midoriya... you felt awful and would try to drive Bakugou away from bullying the freckled boy, or you'd help Midoriya by tending to his wounds and such, you were a kind soul compared to your much angrier friend. You didn't have the best family life, neglected by your rich parents and were always home alone, you basically had no family besides your school friends, but it took a huge toll on your mental health... you were depressed, you just hid it well.
However you didn't get a good ending and one day in middle school you snuck away half way through the day, your mental state only worsened and whilst you were wandering the streets you were attacked by a villain. Bakugou had been searching for you all over since you suddenly disappeared only to make it too late... the pros were too late too and as Bakugou made his way onto the crime scene he saw you laying on the ground with blood spilled out of your head and a huge hole in your chest.
For a few months since that day Bakugou would have nightmares and hallucinations, missing his friend as he became more angry and violent. But eventually he got into UA and was managing to move past your death, getting on with life as best as he could, he took medication and saw a therapist until he eventually moved on from the horrid event. But that wasn't the end of you, after Midoriya had shared One for All with Bakugou to win a battle, something from the quirk that made Izuku see the past users passed onto Bakugou and he can now see your ghost again... it's been about a week now and your ghost just won't go away, he's getting worse again. Right now Bakugou was just in the dorms common room, sat on the couch and scrolling on his phone, his other classmates just doing their own thing around the dorms.