Well, a really interesting plot might be a crossover within the Shugo Chara universe. Sakura could meet other characters from different parts of the Shugo Chara world that she has never encountered before. They could team up to compete in a grand tournament where the prize is a powerful Shugo Chara egg that has the ability to grant one wish. Along the way, they face various opponents and learn more about each other's strengths and weaknesses.
A possible plot is a time - travel plot within the Sakura Haruno Shugo Chara fanfiction. Sakura could be sent back in time to when the first Shugo Chara was created. There, she could learn the true origin of the Shugo Chara and use that knowledge to solve a current crisis in her world. Maybe she discovers a long - forgotten power that can save her friends and the Shugo Chara world from destruction.
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 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.
Amu Hinamori would be a great character to pair Sakura with. Amu has her own set of Shugo Chara and a strong personality. Together, they could share their experiences with their Shugo Chara and learn from each other. Their different yet complementary personalities could lead to some really interesting interactions and adventures.
One idea could be exploring the backstories of the Guardian Characters in more depth. For example, how did they come to be and what were their experiences before they became Guardian Characters.
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.
One plot idea could be that Miki and Kiseki get lost in a mysterious dream world together. They have to work as a team to find their way out while facing various challenges that test their friendship. For example, they might encounter strange creatures that can only be defeated by combining Miki's artistic skills and Kiseki's logical thinking.
One idea could be a male OC who has a unique Shugo Chara that represents his love for art. He could use his art skills and the power of his Shugo Chara to help his friends when they face difficult situations at school, like bullies or tough exams. Another idea is a male OC from a different country who comes to the Shugo Chara world and has a Shugo Chara based on his homeland's culture. This could lead to interesting interactions as he shares his different perspective with the other characters.
One idea could be a crossover where the characters from Naruto and Shugo Chara meet in a strange new world. They could team up to fight a common enemy that threatens both their universes. Another idea is to focus on a character from Naruto who suddenly gains a Shugo Chara. For example, Naruto could have a Shugo Chara that represents his dream of becoming Hokage in a more physical and guiding 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.
A more adventurous fanfiction could involve Yoru and Miki going on a journey through different dimensions in search of a special crystal that has the power to grant any wish. Along the way, they encounter strange creatures and have to rely on each other's unique abilities to survive and reach their goal. Their relationship evolves from comrades to something more romantic as they face numerous perils together.