Ace's death can be said to be the thing I regret the most besides Itachi and Sasuke. I have always thought about how a child was born and grew up carrying the curse and malice of the world. It can be said that without Luffy and Sabo, Ace might have gone astray, wouldn't have met his father and his friends, and might not have died, but I think it would have been unhappy.
So I wanted to give him support, a half that is connected to him by blood, carries the same curse, and has a different bond from Luffy, Sabo and the others. I think Ace deserves a better future, at least not dying in front of Luffy and causing him pain.