The angel bloodline might be neglected in the fanfiction due to the lack of connection to the existing Naruto lore. In the Naruto world, there are already established power systems and lineages. If the angel bloodline is not carefully tied to these existing elements, it may be pushed to the side. Additionally, the writer might be saving it for a big reveal later in the story, so it appears neglected in the early parts.
One possible reason could be that the author wants to focus on Naruto's growth through his own hard work and determination rather than relying on his bloodline. It adds more drama and makes his achievements seem more earned.
A possible plot is that Naruto is constantly bullied because of his neglected state and his unknown bloodline. As he grows, he starts to show signs of his bloodline powers, which attracts the attention of both friends and foes. His journey then becomes about controlling his powers and dealing with the past neglect of his parents while also facing the new challenges that come with his revealed bloodline.
Another possible ability could be purification. The angel bloodline might be able to purify corrupted chakra or evil spirits. In the Naruto universe, there are many instances of dark forces and cursed chakra. A character with this bloodline could be the key to cleansing such malevolent entities. For example, they could purify a village that has been infected by a dark curse or a powerful demon's influence.
One way could be through a sudden discovery during a dangerous mission. Maybe he gets injured and his body's natural response activates some latent aspect of his bloodline.
Well, it might feature characters like Karin. She has a special ability related to her blood, but in the main series, she's not always in the spotlight regarding her bloodline. In fanfiction, her bloodline could be explored more deeply, perhaps showing new aspects or how it could be developed further. Another could be Kiba. His Inuzuka clan has its own bloodline, but compared to some others, it might be considered less explored in certain ways. Fanfiction could give his bloodline more significance and unique developments.
One common theme could be the underappreciated potential of certain bloodlines. For example, a minor bloodline that has unique abilities but is overlooked in the main Naruto storyline might be explored in depth. It could also involve themes of discrimination against those with less - known bloodlines.
One possible story could be that Naruto discovers his unique bloodline abilities later in life and realizes that his parents' neglect was partly due to fearing his power. He then has to come to terms with this and learn to control his abilities on his own.
Perhaps he's been influenced by someone who gives him bad advice. For example, if someone tells him that natural talent is enough and training is overrated. Also, he could be dealing with some personal problems, like a conflict within his family or among his friends that takes up all his time and mental energy, causing him to neglect training.
He might start to rely on his friends more. For example, Sasuke and Sakura could become his main source of emotional support. He would focus on training with them and sharing his feelings, which in turn helps him to grow stronger and more independent.