Tense problem

係，因為once upon a time 係講緊以前ge 事，所以要轉曬變成past tense，has
been都要變成 had been！
希望可以幫到你 ^.^
*重有咩tense ge 問題歡迎隨時問我*

小心 direct speech.

如果是 direct speech, quotation marks 內的 has been 不用轉
例如:
Once upon a time, .... She said, "The King has been good to us".

如果轉去 reported speech, has been 要轉 had been

Yes. We use past tense for story writing.

你說得非常對，無錯！