Maybe in the fanfic, they could find out they're having a baby during a time of chaos in their town. Yusuke has to balance protecting the town and taking care of Keiko during her pregnancy. Their friends could also play important roles. For example, Kuwabara could be the over - enthusiastic uncle - to - be, always bringing gifts for the baby even before it's born.
In the fanfic, Yusuke and Keiko might decide to move to a quieter place for the sake of their baby. They could find a small house near a forest. Yusuke would learn how to build a crib for the baby from scratch, with some comical mishaps along the way. And Keiko would start a small garden to grow fresh vegetables for their new family.
One idea could be that they struggle at first with the news of Keiko being pregnant. Yusuke, being his impulsive self, might initially panic but then quickly step up to support Keiko. He could start taking odd jobs to save money for the baby. Keiko, on the other hand, would be the calm and organized one, preparing for the baby's arrival by reading all the parenting books she can find.
One plot idea could be that Demon Yusuke has to protect Keiko from other demons who see her as a way to get to Yusuke. Another could be Yusuke trying to balance his demon side with his relationship with Keiko, like when he has to hide his new powers and instincts from her at first. Maybe there could also be a plot where Keiko discovers a way to temporarily become a demon herself to be closer to Yusuke's world.
Yusuke would likely become more withdrawn. He was always a bit of a rough - around - the - edges character, but Keiko's death would make him more somber. He might lose his sense of humor that he sometimes showed around her.
Another theme is sacrifice. Yusuke has sacrificed a lot in his life, and Keiko is often by his side. Fanfics may show how they both make sacrifices for each other and for their relationship. For example, Yusuke might sacrifice his time or safety to protect Keiko, and she might sacrifice her own desires for Yusuke's well - being.
To write this fanfic, you need to understand the characters well. Yusuke is tough on the outside but has a soft heart. Keiko is strong - willed and intelligent. Use these traits in the story. For instance, when they face difficulties during the pregnancy, Yusuke might want to solve them with his fists at first, but Keiko would remind him to think rationally. Also, add some cute moments, like Yusuke feeling the baby kick for the first time.
One possible plot could be that Keiko is caught in the crossfire of a demon battle that Yusuke is involved in. Yusuke, being a spirit detective, has many enemies. Maybe a powerful demon targets Keiko to get back at Yusuke. After her death, Yusuke could go into a deep state of despair and vow revenge. He might journey to the spirit world to find a way to bring her back, facing numerous challenges along the way.
One idea could be that Demon Yusuke has to protect Keiko from other malevolent demons while hiding his true nature from her at first. As the story progresses, Keiko discovers his secret and has to come to terms with it. Another plot could be a time - travel scenario where Yusuke goes back in time to save Keiko from a danger that she faced in the past, which changes the course of their relationship in the present.
One idea could be that Gohan takes a break from his Saiyan training to focus on being a good father. He might teach his child about the importance of using their powers for good. Videl, on the other hand, could share her skills in martial arts with the child as they grow up.
Yusuke might cope by throwing himself into his work as a spirit detective. He could try to distract himself from the pain of losing Keiko by taking on more and more dangerous cases. This would be his way of running away from his emotions at first.
One way the story could develop is that Yusuke goes into a deep state of grief and denial at first. He might start to isolate himself from his friends and the spirit world as well. He could be haunted by memories of Keiko and constantly wonder if there was something he could have done to prevent her death.
One great 'yusuke x keiko fanfic' could be 'The Unspoken Bond' which delves deep into their relationship. It shows how Yusuke's rough edges are softened by Keiko's gentle nature.