Japanese DictionaryDefinition of フラグが立つ
- (exp, v5t) (comp) to have a flag set (indicates the setting of a variable that determines, for example, how a game will end)
ちなみにここ一週間は、例えばフラグが立っていようとも、Ｈシーンが無い事は確定事項だからな。暫くの間、辛抱な！
By the way, this week - no matter what flags are set - it's a certainty that there will be no ecchi scenes. You'll just have to bear with it a while.