There is a description of the NAMI Champion role in the NAMI FAQs:
Part of building the NAMI team is identifying a NAMI Champion for the district, a leader who will promote and manage the initiative, foster execution and report results. The NAMI Champion works side-by-side with the district governor team, GAT coordinators, region/zone chairpersons, and other district leaders on plan development, implementation and accountability.
There is also more about a typical NAMI Champion in the Build a Team presentation:
NAMI Champion – the point person for leading this initiative. It could be the District GMT Coordinator, a Past District Governor or another respected leader. A NAMI best practice is to be clear what we expect from team members. For example, we could expect the NAMI Champion to communicate about the program and be its lead supporter; maintain the plan the team creates; keep track of goals vs. actuals and be the go-to person when problems arise.
We recommend district leadership teams discuss this key role. For example, a district team could decide that the district governor will be the chief NAMI communicator, rather than the champion. Variations are fine as long as agreement is reached on what will work best for a district.