YOU SAID:
Nagito could cut off my arm any day.
INTO JAPANESE
渚は、いつの日か腕を切り落とすことができた。
BACK INTO ENGLISH
Nagisa was able to cut off her arm one day.
INTO JAPANESE
渚はある日腕を切り落とすことができた。
BACK INTO ENGLISH
Nagisa was able to cut off her arm one day.
That didn't even make that much sense in English.