I think it isn't. It seems to be a fictional creation with made-up plots and characters.
Well, as far as I know, 'One Day' is not based on a true story. It's more of a creative work crafted by the writers' imagination and storytelling skills. There are no real-life events or people directly linked to it.
No, 'One Day' is not based on a true story. Usually, if it were based on real events, there would be clear indications or mentions. But in this case, it's purely a fictional show.