The fanfic could be set during a time when their village is under threat. Tenten and Sakura have different ideas on how to defend it. Tenten believes in a more offensive approach using her weapons, while Sakura thinks a defensive strategy combined with her medical skills to keep the ninja force healthy is better. This leads to a conflict between them that evolves into a 'vs' situation where they both try to prove their methods are superior.
One possible plot could be a friendly sparring match between Tenten and Sakura. Tenten, known for her weapon skills, might challenge Sakura to a fight to test their respective strengths. Sakura, with her medical ninjutsu and brute force, would accept. They could start off evenly matched, but as the fight progresses, Sakura's strategic thinking and Tenten's unique weapon combinations could lead to an exciting and unpredictable outcome.
Maybe in the fanfic, it's a competition for a rare ninja tool. Tenten is naturally interested in it for her collection. Sakura, on the other hand, realizes its potential use in her medical ninjutsu research. So they end up in a sort of battle where they have to outwit each other to get the tool. Tenten uses her agility and knowledge of weapons, while Sakura uses her intelligence and combat skills.