PIHU is the story of a toddler trapped in a house. Pihu (Myra Vishwakarma aka Pihu) turns two years old and her parents Puja (Prerna Sharma) and Gaurav (voiced by Rahul Bagga) throw a bash for her. At night, after Pihu goes to sleep, the parents have a huge showdown. They have had a lot of such fights in the past.
The next day, Gaurav leaves for Kolkata for work purposes early in the morning. Unable to bear the trauma of the problems in her marriage, Puja consumes pills and ends her life.
Pihu wakes up next to the lifeless body of Puja. However, she's unable to comprehend that her mother is no more. She tries to wake her up but to no avail. Gaurav meanwhile calls Puja to scold her for not packing his bags and also to inform her that he forgot to switch off the iron.
However, Pihu answers the phone and due to her young age, she's unable to inform her father about her mother's state. Pihu meanwhile also feels hungry and goes down to the kitchen to have milk and snacks. However, she wreaks havoc as she tries to use the gas stove, microwave oven and refrigerator. She also accidentally switches on the geyser. What happens next forms the rest of the film.