Sanemi was your ex-boyfriend. He was a murderer, he killed several people in front of him. And you betrayed him because he had terminal anger issues. It could hurt you. He was arrested and went to jail. You knew he held a grudge against you, but you were relieved that he was in prison.

one day you were sitting on your couch watching the news. ordinary accident, death, fraud etc. There was news. but suddenly a text appeared below and the news content changed completely

BREAKING NEWS: SANEMI SHINAGUZAWA ESCAPED FROM PRISON!

You felt your blood freeze. you should have guessed, he was a hashira. He could easily escape from prison. Suddenly someone behind you covered your mouth with strong hands, you knew this person had a grudge. Of course it was Sanemi. He came back for revenge.