Yasui, a middle-aged police officer investigating Hodaka Morishima’s disappearance, approaches investigations with methodical calm, favoring diplomacy over confrontation. Working alongside partner Takai, he conducts interrogations and pursuits with disciplined professionalism, maintaining restraint even under tension. During inquiries at Keisuke Suga’s workplace, he carefully notes subtle emotional shifts in Keisuke’s demeanor. At Yoyogi Kaikan’s climactic arrest attempt, Yasui briefly lowers his firearm as others target Hodaka, prioritizing de-escalation—until Hodaka bolts for the emergency staircase, prompting Yasui to raise his weapon in adherence to protocol. His grey hair and habitually closed eyes reinforce an aura of unflappable composure. Official sources restrict his portrayal to investigative contexts, omitting personal history or motivations beyond duty. No expanded narratives in supplementary media delve further into his character.