Shun Midorikawa is an energetic A-rank Attacker in Border's Kusakabe Squad, recognized for his short stature, unruly brown hair reaching his chin, and distinctive green eyes. He sports two Border uniforms: an early white variant with black collar stripes, sleeve tips, and pant accents, worn casually unfastened with goggles draped around his neck; later adopting a sleek Kusakabe-specific black jacket featuring gold upper sleeves, white detailing, the squad emblem, and gold boots.

His personality radiates competitive exuberance, often likened to an eager puppy showcasing its skills. This drive leads him to publicly defeat Osamu Mikumo ten consecutive times and visibly fume during repeated losses to Yūma Kuga before conceding Yūma's prowess. Despite this showmanship, Midorikawa strategically analyzes opponents mid-combat. He harbors profound admiration for Yūichi Jin, whose past rescue of him sparks hyperactive, almost goofy behavior around Jin and a steadfast ambition to join Tamakoma Branch.

As an Attacker, Midorikawa blends aggressive flair with tactical precision, noting adversaries' capabilities like Tetsuji Arafune’s shift to Sniper eight months earlier while still wielding Kogetsu effectively. His combat insight surfaces in declarations such as "Those who think they'll win are full of openings," aimed at Lamvanein during the Large-Scale Invasion. He habitually coins nicknames for others.

Trivia highlights include his name's meaning—"Shun" signifying "spirited horse," "Midorikawa" translating to "green river," aligning with his eye color. He favors grilled meat, rank-war victories, and Jin.