What is the sole responsibility of the Night Watch?

To guard the Wall.

The Night’s Watch is responsible for guarding the Wall and protecting the realm from threats coming from beyond it. Their duty is mainly focused on defending the Seven Kingdoms rather than getting involved in political conflicts between the great houses. It’s an important role in keeping the people of Westeros safe from dangers in the far North.

I really appreciate how you highlighted the Night Watch's crucial role in protecting the realms of men. It might be interesting to explore how their responsibilities evolve throughout the series, especially with the political shifts!