A robot face is all it takes
Nebula, although she was always an oddball, has made great strides since Guardians of the Galaxy. She's now one of the most beloved characters in the MCU and her journey to Gamora is one the best parts of Endgame.
First is the way she looks on the comics. They show her looking like a giant Luphomoid, with blue and purple skin. She was, however, a very different creature in the olden days and has had many different incarnations.
She was also a pirate, so she had many adventures in the universe. In some of the more epic Marvel stories, she even fought against the Skrulls.
Thanos was Thanos’ father in MCU. He was also her uncle. However, she didn't actually have any family with him. During their time together, they got into all kinds of trouble with various enemies -- even though they had no real connection other than the fact that they were both mercenaries.
It was a difficult relationship for her with Thanos, which ended up being her greatest enemy. Despite showing loyalty to her adopted father, she resented him and his constant use of her as a weapon against others.
As her resentment grew, Nebula was forced to compete with her sister Gamora in combat, and when she beat her, Thanos would maim her and replace a part of her body with robotic enhancements. As she grew older, the resentment got worse and she began to dislike Thanos.
Although she was able to make amends to her sister, she still had problems with Thanos' adoption and other things that Thanos did. This led her to become an unwilling ally of Guardians and turn against Thanos.
It is clear that she was a strong character in MCU. In fact, she was one of the Guardians' first members. She's also a prominent character in Endgame.
It is also surprising and unplanned that her transformation into a hero occurs. It is also possible that she will be Thanos' last death, as she claims at the end.
How she became an iCyborg
In the MCU, Nebula was originally an alien with blue and purple skin, but she was made a cyborg thanks to Thanos' evil brain. She was then subject to all kinds of surgery, bionic enhancements and other strange stuff.
What she went through during the MCU
In Guardians 2, Nebula tells us that Thanos used her and her sister Gamora to punish the winner of their fighting matches. He would take a piece of their bodies, and then replace it with some type of robotic enhancement. It made them both look terrible.