Kouta Shingyoji is a supporting character in the romantic comedy anime Midori Days. He is introduced as a childhood friend of Midori Kasugano, the girl who finds herself mysteriously shrunken and attached to Seiji Sawamura's right hand. Kouta and Midori share a long history, and he has harbored unspoken romantic feelings for her for a considerable time. He attends Ogurabashi High School as a first-year student, making him a classmate or schoolmate of the main cast.

In terms of personality, Kouta is portrayed as a gentle and somewhat meek individual. His character design emphasizes a soft, boyish appearance, which unfortunately makes him a frequent target for bullies. This vulnerability plays into the story, as it is through being rescued from this harassment by Seiji that Kouta's feelings begin to shift. He is earnest and loyal, though his emotions can become obsessive. He develops a strong, comedic fascination with the miniature Midori after learning her secret, and his attempts to interact with her in her tiny form border on fixation.

Kouta's primary motivation initially stems from a desire to support Midori. Upon discovering her crush on Seiji, he arranges a meeting to reveal this to the delinquent, hoping to help his friend. However, his own feelings become complicated when he starts developing romantic attraction toward Seiji, a transformation triggered by Seiji's acts of physical defense on his behalf. This new infatuation creates a comedic love triangle dynamic, as the miniaturized Midori grows flustered and jealous watching Kouta pine for Seiji.

His role in the story is both a catalyst and a source of romantic tension. Early on, he serves to deliver key information about Midori's affections. Later, he becomes one of the few people privy to the bizarre hand-girl secret. He shifts from a potential rival for Midori's affection into an unlikely rival for Seiji's attention, all while serving as an ally who occasionally provides help.

Kouta's key relationships center on his evolving dynamic with Midori and his newfound admiration for Seiji. His childhood friendship with Midori is marked by his unrequited love, which gradually redirects inward as he comes to terms with her devotion to Seiji. Toward Seiji, his feelings intensify from gratitude to a blushing, awkward crush that often leaves him flustered. Seiji, for his part, remains largely oblivious and somewhat unnerved by the attention.

Developmentally, Kouta progresses from a pining, shy admirer of Midori into a more outgoing participant in the central group's chaos. His shifting affections highlight his capacity for emotional growth, even if it leads to humorous complications. He moves from being an outsider who delivers a message to an insider who actively engages with the impossible situation.

Notable abilities include a talent for sewing and crafting doll clothes, a hobby that stems in part from his obsession with a fictional anime character named Ultra-Marin, for whom he carries a doll and creates outfits. This skill proves unexpectedly useful when he learns of Midori's condition, as he begins providing her miniature self with new clothing. The combination of this creative skill and his overall resourcefulness makes him a modest contributor to the makeshift solutions that sustain the series' unusual premise.