Let go of the discussions surrounding the sleep disorder or the romantic scenes; Naan Sigappu Manithan is primarily about one man’s pursuit of retribution. Similar to Thiru's earlier film, Samar, where the protagonist searched for the forces shaping his life, this movie centers on a hero tracking down the unknown individuals who have assaulted and harmed his girlfriend. Like Ghajini, which this film loosely emulates, it attempts to mask the conventional nature of its storyline by giving the main character an unusual medical condition; whereas Ghajini’s hero experienced short-term memory loss, here, the protagonist suffers from narcolepsy. Thiru effectively develops a strong initial portion, utilizing the sleep disorder to generate humor, romance, and a surprising plot development. He guides us through the life of Indran (Vishal), who has narcolepsy, showing how this condition impacts his existence—falling asleep during job interviews after being offered a position, fainting when a classmate proposed to him in school, finding his inability to have sex amusing at a college demonstration, always needing someone ('driver' Jagan plays the hero’s clever friend) to transport him, and, on one occasion when he decides to go out alone, a car horn causes him to fall asleep in the road, which leads to an encounter with Meera (Lakshmi Menon, portraying an angelic figure for this 'imperfect' hero). These scenes, along with Saranya Ponvannan’s portrayal of a somewhat innocent mother, contribute to the film's lighter moments, and Thiru makes us connect with the people in Indran's world. While Ghajini’s hero had tattoos to assist his memory, Indran creates a list—ranging from staying awake all day to kissing a girl and even seeing a Shakeela movie on its opening day—of things he cannot (but desires) to do. As Meera enters his life, he manages to cross off many of these items, and when we realize that only one remains—to fight for what is right—we anticipate how this development will occur. This unfolds when unidentified men stop their car on an unfinished overpass. Indran loses consciousness, while Meera, who is now pregnant with his child, is violently assaulted and falls into a coma. He then resolves to find the attackers and avenge her. But can he, given his condition? There's some ingenuity in the script, such as the hero’s name hinting at the element that could alleviate his condition (resulting in a cleverly executed romantic scene with Meera and Indran). However, Thiru falters somewhat in the second half, introducing too many explanations for why Meera was targeted. We are given a backstory involving one of Indran's friends, adultery, and blackmail, but this segment becomes unintentionally humorous because of how characters shift allegiances and the unconvincing performances from actors who seem out of place. Even the conclusion, despite showcasing some graphic deaths, doesn’t fully convey Indran’s anger toward those responsible for harming his girlfriend; instead, we are left with a sense of mild disappointment, as an intriguing concept is diminished into a standard revenge story.

Source on TMDB