Ōta-kun is a middle-school student whose face visibly betrays his emotions at all times, an involuntary trait leading to frequent teacher discipline for "giving it away." This expressive nature defines his interactions. Academically indifferent, even to single-digit test scores, he actively seeks amusement through mischievous schemes targeting his classmate Kashiwada-san. These attempts to disrupt her placid demeanor or scare her consistently backfire.

His emotionally transparent, clownish personality stands in direct contrast to Kashiwada-san's inexpressiveness. Initially captivated by her unchanging expression, his persistent efforts to provoke a reaction gradually transform into mutual romantic feelings. Despite her own lack of visible emotion, Kashiwada-san becomes uniquely able to interpret his expressions. This evolving dynamic forms his core character development, shifting from playful antagonism to genuine affection and understanding.

Ōta-kun interacts with classmates including Tadokoro-kun, Sata-kun, Tabuchi-san, and Odajima-san. Among them, Odajima-san is noted as perceptive regarding Kashiwada-san's subtle cues, though Ōta-kun remains central to Kashiwada-san. His social circle and school experiences provide context for his expressive nature and comedic mishaps.

The progression of his relationship with Kashiwada-san continues beyond the original manga into the spin-off series *Inexpressive Kashiwada and Expressive Oota+*, exploring their interactions and emotional bond further.