Perhaps a plot where Tadase loses his memory and Amu has to help him remember who he is. She shows him all the things they've done together in the past, like their school events and their battles against the X - Eggs. As she does this, Tadase starts to fall in love with her all over again, but in a new and different way.
One idea could be that Tadase and Amu go on a magical adventure together within the Shugo Chara world. They might encounter a powerful new enemy that only their combined powers can defeat. This could involve a lot of action scenes where they fight side by side, and in the process, their relationship deepens.
In a Shugo Chara Amu x Tadase fanfic, it could be a story where they are paired up for a school project. At first, they struggle to work together because of their different personalities. But as they start to understand each other better, they realize they make a great team. Along the way, they also have some cute moments that show their growing affection for each other.
A plotline could be that Amu and Tadase get transported to a parallel universe where their roles are reversed. Amu is now the cool and confident one while Tadase is the more shy and reserved. This would create an interesting dynamic as they have to adapt to these new personalities and still find a way to get back to their original world.
A great plot idea could be that Amu and Ikuto are chosen to participate in a special Shugo Chara tournament. They must compete against other pairs from different regions. Along the way, they face various challenges that test not only their physical and magical abilities but also their relationship. As they progress, they start to realize their feelings for each other are growing stronger and this affects their performance in the tournament in both positive and negative ways.
Their relationship could develop through shared experiences. For example, they could work together on a school project. During this time, they would get to know each other better without the pressure of their Guardian duties. They might discover new things about each other like their hobbies and dreams, which would bring them closer.
Perhaps a fanfiction where all the Shugo Chara characters swap their guardians. So, a normally calm and collected character gets a hyperactive Shugo Chara to take care of, and vice versa. This would lead to a lot of comical situations as they adjust to their new roles and the different personalities of the Shugo Chara.
One great 'Shugo Chara! Amu x Kairi' fanfiction might be those that explore their relationship development. For example, some stories could focus on how they support each other during the challenges in the Shugo Chara world. They might face difficulties with the X - Eggs or other antagonists, and through these experiences, their bond grows stronger.
One common theme is friendship evolving into something more. Since Nagihiko and Amu have a connection in the original series, fanfictions often explore how their relationship deepens romantically.
One possible fanfiction could be about Amu's journey while pregnant and how she still tries to maintain her normal life in the Shugo Chara world. Maybe she has to deal with the reactions of her friends and guardians.
One idea could be a crossover with a magical girl anime like Sailor Moon. The Shugo Charas could team up with the Sailor Scouts to fight a common enemy that threatens both their worlds. For example, an evil force that wants to steal the power of both the Heart's Eggs and the Silver Crystal.
One possible plot could be that after the kiss, they have to face the reactions of their friends. Some friends might be supportive while others are shocked. For example, Amu's friends could initially be a bit taken aback but then come to accept their relationship as they see how happy Amu and Ikuto are together.