"Tanaka-kun wa Itsumo Kedaruge" centers on Tanaka, a high school student who embodies lethargy to an extreme degree. His primary goal is to live a life of minimal effort, often dozing off or spacing out during class. Despite his seemingly indifferent demeanor, Tanaka is not disliked by his peers; instead, his laid-back personality attracts a variety of friends who find his behavior oddly endearing. Among them is Ohta, Tanaka's loyal and physically imposing classmate, who frequently carries Tanaka around when he is too tired to move. Ohta’s dedication to Tanaka’s well-being often leads to comedic situations, as he goes out of his way to accommodate Tanaka’s laziness.

The series unfolds in a slice-of-life format, with episodic chapters focusing on the daily interactions between Tanaka and his classmates. Miyano, a bubbly and energetic girl, becomes fascinated with Tanaka’s lethargic lifestyle and aspires to emulate his calm demeanor, though her efforts often result in humorous failures. Echizen, a quiet and stoic girl, occasionally joins the group, adding a contrasting dynamic with her reserved nature. Shiraishi, the school’s popular and beautiful idol, also becomes part of Tanaka’s circle, drawn to his unassuming personality and finding solace in his lack of interest in her fame.

Throughout the series, Tanaka’s interactions with his friends highlight the contrast between his desire for a quiet, uneventful life and the lively, often chaotic energy of those around him. Despite his constant attempts to avoid exertion, Tanaka inadvertently becomes a central figure in his friends’ lives, offering them a sense of stability and calm. The narrative explores themes of friendship, individuality, and the value of taking life at one’s own pace, all while maintaining a lighthearted and comedic tone. The characters’ relationships evolve naturally, with each individual contributing to the group’s dynamic in unique ways, creating a balance between humor and heartfelt moments.