O2 is a survival drama film written and directed by GS Viknesh and produced by SR Prabhu and SR Prakash Babu under the banner Dream Warrior Pictures. The film stars Nayanthara and Rithvik in the lead roles while Barath Neelakantan, Rishikanth and others play crucial supporting roles. The film has music by Vishal Chandrasekar and cinematography by Thamizh A Azhagan.

Veera (Rithvik) is a kid with a medical issue in his lungs, which makes it difficult for him to breathe without an Oxygen tank. His mother Parvathy (Nayanthara) has to take him to Cochin so that his lung disease is treated. During the journey, their bus gets stuck underground due to a landslide. How they manage to survive nature's onslaught forms the rest of the film.

O2 starts off with an animation sequence where a bird flies across all sources of pollution such as factories, dumpyards, roads with heavy traffic and drops a small plant in a flower pot. And then a small kid starts taking care of it on a daily basis. This makes us all think that the film is based on a message to save nature.

But barring an explanation by Nayanthara at the start of the film, there seems to be little logical connection between the film and the message it wants to convey. The screenplay lags at many places, mainly due to the majority of the story is happening inside a bus. This doesn't mean that the film is bland in any sense.

The film solely relies on Nayanthara and Rithvik's brilliant performances. Their chemistry is superb and is probably the only thing that keeps us invested in the proceedings. Barath Neelakantan plays the role of a menacing police officer whose character comes across as irritating, but his performance is solid.

The music by Vishal Chandrasekhar supports the visual that is choas and intense. The cinematography and editing by Thamizh Azhagan and RK Selva respectively, create a bit of suspense and tension when the civilians are trapped under the rocks. The VFX could have been better as well.

Overall, director Viknesh has tried to take the famous philosophical 'Lever and Trolley' question and make a film having it as the base. There are good moments at regular intervals and the film has good potential as well. However, the engagement could have been better so that the potential of the script is completely tapped. Nevertheless, the film is a harmless one time watch with a message on protecting the environment.