One idea could be a story where Hei has to protect Misaki from a new, powerful enemy that is after her because of her knowledge of Contractors. This would put them in a lot of dangerous situations and force them to rely on each other more than ever.
A plot could involve Misaki somehow getting Contractor abilities. This would change her relationship with Hei as she starts to understand his world better. They could then team up to fight against the Syndicate, who wants to control Misaki's new powers. It would be full of action and exploration of their changing relationship.
A plot idea could be that there is a strange phenomenon affecting Contractors and Dolls, and Misaki and Hei are the only ones who seem to be immune at first. They then have to investigate the cause while also dealing with the suspicion and fear from others in their respective communities. As they dig deeper, they find out that it has something to do with an ancient and forgotten power that is starting to resurface.
One idea could be exploring Hei's past in more detail. Maybe a story where he has to face a threat from his old organization that forces him to remember things he'd rather forget. Another could be a fanfiction where Hei teams up with an unexpected ally, like a character from a different anime universe, to solve a mystery in the Darker than Black world.
Perhaps a plot where an outside force tries to manipulate Hei and Yin's relationship. They have to figure out who is behind it and in the process, they learn more about their own feelings for each other. This could involve some intense action scenes as they are constantly under attack while trying to solve the mystery.
A lot of fanfictions focus on the idea of redemption. Maybe Hei has done something in the context of the story that he needs to make up for, and Misaki plays a role in that process. Also, there's the theme of hidden feelings. Since their relationship in the original anime is somewhat ambiguous, fanfictions like to explore if there are unspoken emotions between them. For example, they might be secretly in love but unable to express it because of their circumstances.
The relationship could be developed uniquely if Hei has to protect Misaki from a threat that is specifically targeting her because of her connection to him. This would make Hei more open about his feelings towards her.
Well, another option could be to check out some dedicated anime fan forums. There are often threads where fans share and discuss their favorite fanfictions. You could search for ones related to Hei and Misaki from 'Darker than Black' in those threads. Some popular anime forums might be Anime Planet's community section or Reddit's anime - related subreddits.
Fanfiction writers could explore their pasts more. Maybe there are events in their childhoods that are similar or that connect them in some way. By delving into these, their relationship can be developed on a deeper, more personal level. They could also have more heart - to - heart conversations that expose their true feelings for each other.
The plot might start with an introduction of their relationship, whether it's one of mistrust or an immediate connection. Then it could develop as they face various challenges together, perhaps related to the world of Contractors. As the story progresses, their bond may strengthen or be tested in different ways.
The unique world - building of the original work also contributes. The concept of Contractors and their powers is fascinating. Fanfiction can play around with these powers, creating new power combinations or exploring the limits of existing ones. For example, a fanfic could show a Contractor with a never - seen - before power and how it affects the balance in the 'Darker than Black' world.
One great 'Darker than Black - HEI Crossover' fanfiction is 'The Unlikely Alliance'. It brings together characters from different arcs in a really interesting way. The author does a good job of maintaining the personalities of the characters from the original series.