Tom: ‘Mary, when I return from this war, would you consider marrying me?’
Mary: ‘Oh my God… Tom, what you’ve just said is ‘死亡フラグ’ (death flag)!’
死亡フラグ (しぼうふらぐ, shiboufuragu) is a Japanese slang term that literarily means ‘death flag’. It describes a clichéd event or line in a story which foreshadows that someone is doomed to death in the near future. For instance, as written in the preface, if a man proposes to his partner before enlisting for military service amidst a devastating war, that is a typical ‘death flag’ in a tragic play, suggesting that he will never see her again. Here is another example—imagine that mysterious serial murders are taking place in a small isolated cottage, and people staying there are getting together to discuss how to protect themselves. Then all of a sudden, someone stands up and yells, ‘I don’t f*cking trust any one of you. I’m going back to my room, that’s way safer than being here.’—alas, he/she will most likely be found dead in his/her own room shortly, because that is a typical ‘death flag’ in a clichéd mystery fiction.
死亡フラグ is also used figuratively to indicate an event or line that foretells a catastrophic failure. For instance, when you are pulling an all-nighter to prepare for an exam in the next day and think in your heart, ‘let’s take a nap for 30 minutes to be more productive’, that is a typical ‘death flag’— you will wake up in despair after the exam is over.
General Usage of フラグ
In Japanese slang, フラグ itself can be used to indicate a variety of incidents that suggests what’s happening in the future. In particular, it often indicates ‘a romance flag’: a promising event or line which suggests that you will be in a relationship with someone. For example, if you coincidentally touched someone’s hand at a bookstore when two of you reached for the same book in a shelf simultaneously, that’s a typical ‘flag-on’ moment in a drama or anime. If you notice that such ‘romance flag’ has been turned on, you can say ‘フラグが立った’, meaning ‘A flag has stood’. On the other hand, if you inadvertently neglect such flag, that is ‘フラグを折（お）る’, meaning ‘snap a flag’. For instance, some of you may regret that you ‘snapped a flag’ back in high school when you were too immature to notice your crush giving you the inklings of interest.
死亡フラグ consists of two words 死亡（しぼう）meaning ‘death’ and フラグ meaning
‘flag’. Here, フラグ is a loaned word from a flag in programming, which contains a binary value (true or false) and determines the next step of a program. Therefore, ‘death flag’ means a watershed moment when someone or something are doomed to death or ‘deadly’ failure.
This line is nothing but a ‘death flag’ ( = This line totally suggests someone’s death or fiasco)
Two days before Christmas, she suddenly texted me and I thought it was フラグ (a ‘romance flag’), but it wasn’t at all.
(Note) Christmas is one of the most important days for couples in Japan.
Synonyms:虫の知らせ (premonition)、伏線 (foreshadowing)
Synonyms in English: premonition, a clichéd event or line that suggests someone’s death
Related words and phrases: 死亡 (death), フラグ (flag)