One idea could be a joint investigation. Maybe a case starts in Hawaii but has ties to the mainland where NCIS operates. Agents from both teams could meet, and there could be some friendly rivalry as they try to solve the case. For example, McGarrett from Hawaii Five - 0 and Gibbs from NCIS might have different approaches to interrogating suspects. McGarrett could be more upfront and aggressive, while Gibbs has his famous gut - feeling - led interrogations. Their teams would also bring different skillsets. The NCIS agents are experts in military - related crimes, and the Hawaii Five - 0 team knows the local scene and has connections there.
Another story idea is a character swap of sorts. A member of the NCIS team could be sent to Hawaii on a temporary assignment to learn from the Hawaii Five - 0 team, or vice versa. This would lead to some interesting cultural and procedural clashes. For instance, the NCIS agent might find the laid - back Hawaiian lifestyle a bit different from the more structured military - influenced environment they're used to. And the Hawaii Five - 0 agent could struggle with the strict military protocols when working with NCIS.
A third idea could be a personal connection between the two teams. Maybe an NCIS agent has a long - lost relative who is part of the Hawaii Five - 0 team. This discovery could bring the two teams together in an unexpected way. They could be working on a case that is related to their family history, and the personal stakes would add an extra layer of drama to the story.