I Stole The Story's Second Male Lead

Synopsis

I was walking past an alley when I saw several guys roughing up a young man. Then, out of nowhere, glowing captions flashed in my vision. [OMG our poor second lead is getting beaten up... Someone save him!] [Yesss the heroine's coming! She's totally gonna rescue him!] The heroine? Me? Without another thought, I turned and walked right into the alley. Instantly, the captions blew up. [Wait, who IS this girl?? She's not in the script!] [What is she doing? Someone stop her!]