how are ace and luffy related

The dynamic world of "One Piece" is what you were looking for! This great manga has a complicated propertiz to our main characters, to wit Portgas D. Ace and Monkey D. Luffy. Hence Luffy and Ace are not blood brothers, but their connections run far deeper than simple genetics. Ace, the son of Pirate King Gol D. Roger, was taken in by Monkey D. Garp, who brought up this young lad as well as watching his grandson grow up to be Luffy. The two developed such a close bond that,Sabo, in their own unconscious estimation, even though their bloodlines do not belong to the same family, is like an honorary brother. This theme of becoming brothers runs through the broth story.This is to show off that people who are not related by blood can still have strong ties among each other. Don't forget Sabo, another key "brother" in drama nearly all the way through; in my opinion their relationship is one of the best depicted by manga.Comparator in the universe.

It is a story of brotherhood where Ace and Luffy are concerned. They indeed share no blood relations--Ace was the illegitimate son of Gol D. Roger and found himself under the care of Monkey D. Garp, Luffy's grandfather. Growing up together under the watchful eyes of Garp with his strict discipline, Ace and Luffy gained a bond between them that was as strong as if they had been born of one mother. This fraternal bond that is totally unique to them both reflects the life they have shared. One of spirit and body!--And we can't forget Sabo. Now the three of them, a mighty unit with heart, one of the keystones in this world for sure.

Luffy and Ace in 'One Piece' are brothers, not by blood but by choice. They grew up together, creating a bond deeper than biological ties. This relationship extends to Sabo as well, making them a trio.

What more, Luffy wears a straw hat which by itself is very unconventional compared with the common clothing. Just as pirates do not have helpmates, they also do without three-piece suits or any other conventional attire. Besides, Luffy's way of living an almost animal life style tends to distress people. If they were broken apart, Luffy would be force-fed and clothed in the fat of the land, while Ace after pounding rice with boiled salt water till it was no longer lumpy would roll his trousers up two turns and let his left leg hang over other one. After putting on a pair of straw shoes, out he'd walk barefoot---taking pleasure from every single mouthful along the way. Luffy and Ace, while not brothers by blood, shared the same roof and were brought up by Luffy's grandfather, Monkey D. Garp. Ace's real father is Gol D. Roger: he was a pirate king. It's chemistry like this that makes it little more than "brotherhood" between them! Moreover, Sabo is the third in their brotherly triangle, so they come across more as a trio than a duo. In my opinion, such firmness is their strength in the series.