One popular storyline could be how Chizuru and her partner deal with the upcoming arrival during a time of turmoil. Maybe they have to face challenges from the Shinsengumi's enemies while also preparing for the baby. Another could be a more domestic focus, like Chizuru's pregnancy cravings and how her friends in the group support her through the various stages. And some fanfictions might explore how the baby could potentially change the dynamics within the group.
One interesting storyline could be how Chizuru's pregnancy affects her relationships within the group. For example, the other characters might become more protective of her. They could also struggle with the new responsibilities that come with a coming baby in their midst.
During her pregnancy, Chizuru might develop a stronger sense of purpose. Knowing she is going to be a mother gives her a new goal. This could make her more empathetic towards others who are also trying to protect their loved ones. She may also become more patient as she experiences the slow process of bringing new life into the world and realizes that some things cannot be rushed, which is a big shift from her character in non - pregnant scenarios.
Another theme could be the exploration of their individual characters within the fan fiction. For example, delving deeper into Souji's complex personality and how Chizuru affects or is affected by it. Often, themes of loyalty and sacrifice are also explored as they are important aspects of their characters in the original story.
The news of Chizuru's pregnancy can intensify the plot. It can create a sense of urgency among the characters to protect her and the unborn child. This may lead to them taking more risks or making different decisions than they would have otherwise.
One interesting plot could be Kazama and Chizuru getting lost in a forest together. They start off distrustful of each other, but as they face various challenges like wild animals and difficult terrains, they gradually learn to rely on one another. This could lead to a deeper understanding and the start of a romantic connection.
The forbidden aspect of their relationship can be very alluring. They come from different backgrounds, with Kazama being a powerful demon and Chizuru being a human. In many fanfictions, this creates a sense of tension as they struggle against the odds and the rules of their respective worlds to be together.
One popular storyline could be about how Hana and Naruto support each other during the pregnancy. Naruto, with his positive attitude, might keep Hana's spirits high. He could be constantly getting things for her, like her favorite foods. Another storyline might involve the reactions of their friends. For example, Kiba could be really excited to be an 'uncle' in a sense and might offer to train the baby when it grows up. Also, there could be a plot where Hana has some difficulties during the pregnancy, like morning sickness, and Naruto has to learn how to take care of her and the household.
I'm not sure specifically which are the most popular ones. But generally, you can start by looking on major fanfiction platforms like Archive of Our Own or FanFiction.net. There might be some interesting Ichigo and Chizuru - related fanfictions there, though I can't guarantee the presence of 'lemon' content as it might violate the site's terms in some cases.
Create an interesting plot. It could be a new adventure, a different take on their relationship, or a situation that challenges their beliefs. For example, you could set it during a time when they are separated and have to find their way back to each other, adding elements of mystery and suspense.
One interesting story could be about the characters facing a new supernatural threat that wasn't in the original. For example, a powerful spirit that has the ability to manipulate time. This could lead to some really unique plot twists as the characters have to figure out how to stop it while also dealing with their own internal conflicts.