Arun Vijay is the youngest son of his wide and wealthy family. His brothers are regressive, addicted to their caste. The villain is from the fisherman family, who wants to seek revenge as he has lost his brother a few years back and Arun Vijay is accidentally one of the reasons behind it. A big issue arises that breaks the family, how the hero resolves it all forms the remaining story.
Director Hari has a separate fan base for his way of direction and writing of the story. Most of his movies shows the power of Manliness & Yaanai is not an exemption. The family emotions have worked out really well and it will definitely strike a chord with the masses. The hero protecting his family from the villain is a trope that Hari often resorts to and the director manages to present this with slight variations to make the story not become too predictable.
Anyways, the emotional core of the film needed much more intense sequences to make us root for the characters. The villain character is weakly sketched and there is not even a single percentage of threat posed by him. Yaanai movie is a mixture of action, love and sentiment. The first half moves with clap-worthy scenes, but the second half bit lags.