Taekook_mafia_007 's book has a Good start with introduction of characters.

The story uses dialogue and descriptive language to create a sense of suspense and tension which makes it interesting and emotional.
The main character has a tragic past and a hidden vulnerability. You have also built some suspense and mystery by hinting at his involvement in the mafia and his desire for revenge.

I suggest you to use grammarly to check for punctuations and spelling errors. You can also use some synonyms to avoid repetition of the same words.

You can try describing the emotions and actions of your character. Instead of stating. This would make your readers more engaged and empathetic with your character.

I recommend this book to everyone who likes fanfiction and bts.