Sunset has always wondered who her father is. Her mother, Princess Celestia, described him as kind, but can get very angry when woken up not on his own terms. When the Anon-A-Miss incident rolls around years later, she finally gets her chance to meet him - the Mighty Firebird. He will stop at nothing until those who have tormented his daughter have been punished severely.
The Suicide/Self Harm tag is for when Sunset nearly tries to end it all.