While many fans would argue that if anyone was about to start watching Fullmetal Alchemist you shouldn't even bother with the original 2003 run and jump straight into the Brotherhood remake, there are some things that are just done better the first time. No one expected that to be the iconically tragic arc of Nina and Shou Tucker. The divergence between Fullmetal Alchemist and Fullmetal Alchemist: Brotherhood exists because the former was aired before the manga's completion. The 2003 version had a little more wiggle room in regard to filler, and this proved to be advantageous when it came to the mutilation and murder of Nina Tucker. As opposed to the manga and Brotherhood, Edward Elric and his younger brother, Alphonse, are twelve and eleven and will be studying at the home of the Sewing Life Alchemist, Shou Tucker, as they prepare for Edward's State Alchemist assessments.
Shou Tucker is known for his ability to combine different animals together to make chimeras and received his State Alchemist position because of a chimera that could talk. His next assessment is fast approaching, and his unsettling and slightly threatening nature make him an awkward study partner. Tucker's rising stress hovers over every study session, and if that wasn't a distraction enough, the Elrics end up spending most of their time playing with Tucker's fiver year old daughter, Nina, and her dog, Alexander. The Elrics and Nina spent days together, and when Edward passed his assessment, Nina sat on Alphonse's shoulders at the ceremony. When Ed's birthday came around, the three of them were invited to Maes Hughes' home where his pregnant wife, Gracia, gave birth to Elicia. With Nina present in so many events in the Elrics' lives, her father's continued unsettling behavior catches their attention. Tucker even establishes himself as a threat to Ed and Al's security by correctly guessing the two of them committed the taboo of human transmutation. Tucker's conduct is allowed by the unconcerned military officials, and the Elrics become so worried about Nina's safety, that they break into the Tucker house. They were already too late.
Shou Tucker's New Talking Chimera
Tucker had fused Nina and her dog into a talking chimera, something that is irreversible. In his darkened study, only illuminated by candles, there are transmutation circles scrawled on the floor, the ceiling, and the walls in red ink. When Edward attacks Tucker in fury and despair, Tucker rubs in the fact that science, alchemy specifically, always sacrifice people to make progress. He and Ed are alike in that aspect. As the military came to take the Tucker family away, Ed throws a fit and upends the car allowing for the chimera that is somewhat still Nina to escape and run away into the rainy city.
Just in time to run into a notorious serial killer named Scar who turns them into a blood stain on an alley wall to be found by the two boys who tried and failed to save her life. In the aftermath, Edward tries to resign from the military, is visibly barely holding it together, and getting into fights with his little brother, and this is all technically before Ed has done anything as an official state alchemist.
Now, take away almost all of that in the reboot. Fullmetal Alchemist Brotherhood focuses more on the plot from the manga, that was close to completion by its debut. In Brotherhood, Ed is fifteen when he and Al go to study at Shou Tucker's home to do research on getting their bodies back. Edward willing shares their story of human transmutation with the other alchemist, and the boys meet Nina and play with her.
Shou Tucker
Shou Tucker talks about being worried about his assessment, but Nina and the boys encourage him not to lose hope. When the Elrics come back the next day, they discover Tucker with a new chimera and congratulate him. It wasn't until the chimera calls Edward 'big brother' that the Elrics even realize something is wrong.
Tucker still says his piece about him and Edward being similar, and then the military comes to arrest them both. While Tucker and the chimera were being kept under house arrest, Scar breaks in and kills them both. And this all happens in one episode.
There is no build-up or integration of Nina Tucker in the boys' lives. No tying her to important events and memories. In Brotherhood, her death is unpredictable, and her loss is more focused on her just being a fellow human being, an innocent child, who didn't deserve an end like this. In the 2003 version, the horror is similar, but it focuses on the fact that the audience knows NIna. We've spent multiple episodes with her, and her death is personal not because it was just a little girl, but because it was Nina.
Brotherhood removes time and energy put into the Tucker's while piggybacking off the 2003 version to make the audience care. There's horror in the situation because we don't know these characters enough to be invested. We've barely been with them for 23 minutes. The Elrics are blindsided by her death because there was no way they could have ever expected a father to do that to his child. This episode is a testament to their naivety which is weird considering how the boys are older here and are not new to horror.
Before the Transmutation
The 2003 version effects the audience because Nina was an established character that there was an underlying threat towards from her father the entire time. The regret that comes from a lack of action because the boys knew there was something wrong with Tucker, who survives unlike in Brotherhood, to do more experiments. They were too late because they didn't act fast enough, and that makes it seem like this tragedy could have been avoided if they just interfered sooner.
This happens not only once, but twice when the boys are the first on the scene to Scar's murder of Nina and Alexander. Literally ten minutes before, the boys had seen the chimera alive, and in trying to save them, they drove the chimera towards someone who killed them in such a perfunctory way. In 2003, they're always too late, and there are lasting after effects of Nina's death. In Brotherhood, Ed and Al are sad about it for one episode after, and then they're moving forward on their quest again.
While some people argue that Fullmetal Alchemist: Brotherhood is the only version of the anime that's worth watching, it would be remising to deny that the only reason the death of Nina Tucker became so infamous in the fandom is because of the 2003 anime.