One idea could be that Sakura uses her medical ninjutsu to heal Kankuro after he gets seriously injured in a battle against a powerful enemy. She has to overcome various challenges like limited supplies and the unique nature of Kankuro's puppet - related injuries.
A plot twist could be that the method Sakura uses to heal Kankuro has an unexpected side effect. For example, it gives him a temporary boost in his puppet - using abilities that he has to quickly learn to control.
A possible fanfiction could be set in a post - war scenario. Kankuro and Sakura are part of a group that is trying to rebuild relations between their respective villages. They often have debates on how to best achieve this. Along the way, they also discover that they have more in common than they thought, which leads to a deeper connection between them.
One possible story could be about Kankuro and Sakura teaming up on a mission. In the fanfiction, they start off as just comrades but gradually develop a deeper understanding and friendship. This friendship might then be the base for some interesting character - growth arcs for both of them, like Sakura teaching Kankuro some medical ninjutsu basics in return for him showing her some of his puppet - making secrets.
Maybe there's a plot where Kankuro and Sakura are both chosen to participate in a special ninja tournament. They train together before the tournament, learning from each other's techniques. During the tournament, they support each other and their friendship blossoms as they progress through the various rounds.
One common theme is friendship. Writers often explore how these two characters from different villages can become friends. For example, they might start off as rivals but then find common ground in their love for their respective villages and the shinobi way.
You can start by looking on some popular fanfiction websites like FanFiction.net or Archive of Our Own. They have a large collection of Naruto - related fanfictions, and you might be able to find some that feature Kankuro and Sakura. Just use the search function on the site and type in 'Kankuro and Sakura' to narrow down the results.
One great piece of Sakura Kankuro fanfiction might be 'The Unlikely Bond'. It focuses on their friendship development in an AU (alternate universe) where they are both on a mission together. They start off not getting along but gradually learn to respect and rely on each other.
Kankuro could use his puppet - making skills to his advantage. He could create puppets that are resistant to the elements in the One Piece world, like water - proof puppets since there are a lot of sea - related challenges there. Also, he could make puppets that can fly to deal with the various islands and different terrains.
One great 'Kankuro x Reader' fanfiction is 'The Puppeteer's Heart'. It beautifully captures Kankuro's complex personality. The story starts with the reader accidentally stumbling upon Kankuro's puppet - making workshop. From there, a slow - burning relationship develops. It's filled with moments of Kankuro being both mysterious and endearing.