Lucy is another character that could be prominently featured. Given her gothic nature, she might have an initial attraction or understanding of the dark arts. She could either be a novice trying to learn more or a bit of an expert guiding the other Loud siblings when they encounter dark arts - related situations.
Well, Lucy Loud might be a popular character in such fanfics. Her gothic nature could add an interesting layer to a yandere - inspired storyline. Another one could be Lori Loud. Given her bossy and somewhat controlling nature in the original show, it could be tweaked into a yandere - like behavior in fan - created stories. And of course, there's Lynn Loud. Her competitive and aggressive side could potentially be molded into a yandere - esque character in 'the loud house yandere fanfic'.
There can be original characters created specifically for the fanfiction. For instance, a detective who is obsessed with bringing down the Joker but slowly starts to lose his own sanity in the process. This character can provide a new perspective on the Joker's reign of terror.
Lincoln is often a central character. Since he's the middle child, he usually gets caught in the middle of things and is in a good position to be involved in getting or spreading the message. He might be the one trying to make sense of a confusing message or passing on important information to his sisters.
Obviously, the Loud family members would be the main characters. Lincoln, being the main character in the original series, would probably play a crucial role in this fanfiction too. He might be the one to come up with plans to deal with the situation of being left in the dark.
In Naruto dark chakra fanfiction, Sasuke is frequently a central figure. Given his complex character arc and his inclination towards power - seeking, it's easy to envision him being affected by or exploring dark chakra. Naruto too can be a main character. His strong will and connection to positive chakra could be put to the test when faced with the allure of dark chakra. Another character often involved is Kabuto. He has a history of being involved in dark and underhanded schemes, so it's not a stretch to see him in stories centered around dark chakra. There are also some original characters created by fanfiction authors that are specifically designed to interact with the concept of dark chakra in unique ways.
Naruto himself could be a main character. He might be tempted to use dark summons to gain power to protect his village or friends. For instance, in some fanfictions, he discovers a dark summon that could potentially defeat a powerful enemy threatening Konoha, but at a great cost.
Naruto himself is often involved. He might be either tempted by Dark Hadou or have to fight against those who use it. Sasuke could also be a main character in such fanfictions. His quest for power could lead him to explore the Dark Hadou. And then there's Kakashi, who with his experience and knowledge, might be involved in trying to stop the spread of Dark Hadou.
Well, obviously Dark Silver himself is a main character. Often Sonic might also be involved as he is a central figure in the Sonic universe. Their interactions can create interesting storylines, like a rivalry or an uneasy alliance.
Obviously Naruto himself is a main character as he is the one under the dark control. Then there would be his friends like Sasuke and Sakura. Sasuke might be crucial in trying to understand and counter the dark power since he has his own powerful abilities.
Naruto himself is often a main character. He's usually the one who stands up against the dark guild's evil plans. Sasuke might also be involved, as his power and sometimes ambiguous moral standing can add interesting dynamics when dealing with the dark guild.