Kosuinen, whose real name is Nen Kosugi, serves as the head director of the Skull Lease Northern Ostendel branch and the intellectual core of the Clean Aku trio in the anime Gyakuten Ippatsuman. As the group’s scientist and gadget maker, he designs many of the schemes used to sabotage the rival Time Lease company, though he typically orders the trio’s giant mecha from a separate manufacturer rather than building them himself. He lives alone in a company dormitory, separated from his wife and children; his wife is a spendthrift and he married her largely because she resembled his boss, Mun-Mun.

Kosuinen is known for his short temper and a tendency to become intensely serious when frustrated, at which point a scar appears on his forehead. He often vents his work-related stress to his colleague Kyokanchin and occasionally becomes flustered by his attraction to Mun-Mun, though his feelings are not romantic. Despite his villainous role, he possesses a genuine passion for cooking soba noodles and frequently dreams of leaving the Skull Lease to run a noodle restaurant, a fantasy his boss refuses to indulge.

Among the Clean Aku trio, Kosuinen is the most determined to defeat the hero Ippatsuman. He devotes considerable effort to analyzing the hero’s abilities and devising counters, at one point even creating a parody form called Gyakuten Sanpatsuman and building mecha that mimic Ippatsuman’s own robots. His obsessive planning culminates in a scheme that, with unintended help from another Skull Lease executive, briefly appears to kill Ippatsuman. This seeming victory ultimately proves hollow.

Later in the series, after the Skull Lease collapses and the trio separates, Kosuinen boards a train heading into an uncertain future, implying a desire to start anew. His early life is shown as that of a bratty child who cheated and bullied others, a past he recalls with pride. In addition to his inventive and strategic talents, Kosuinen is a skilled cook and possesses a catchphrase he utters when activating devices. His personal development, though limited, hints at a longing for a simpler life free from constant failure.