Koichiro was an adult Japanese man with short black hair. He's well built and tall, wearing either construction worker clothes or a plain green shirt and jeans.
While installing lights for a stage in a stadium, an earthquake occurs. When everyone confirms they are fine, Koichiro decides they finish the lights and call it a day. Moments later a much stronger earthquake occurs and makes him fall, but his safe ropes save him.
He takes his scooter and heads home, but a building collapses and breaks the bridge he was on. He still reaches home, where he can't find anyone and illuminates a path on a nearby hill for his family to see and come. The first one to come is Ayumu and a bit later Go, who had his eyes bandages. Taking off the bandages, Koichiro comments Go is lucky and only his eyelids are cut and patches them. A moment later Mari also arrives and comments she is glad that everyone is alive and well.
Due to the rising water levels, the survivors decide to leave the hill. Reaching a crossroad, a store owner proposes they go east as the epicenter was in Okinawa and east would be safer, while Koichiro says he heard a report of east sinking. Go contacts his friend, who tell him that west is safer and Koichiro decides his group would go that way. They begin following a road where Ayumu sees an elderly couple that she gives the last of their water, Koichiro optimistically tells her not to worry about it. They reach a store, but it was already looted and after some tremors, he decides they to continue offroad. They reach a river, where they resupply with water and continue following it to a residential area, where a wild boar appears and he manages to kill it and cooks it for dinner. Since Ayumu refused to eat it, on the next day, they find a yams garden that warns people to not dig them out. Koichiro decides to dig some, so that Ayumu could eat, but while he digs, Ayumu reads a warning sign of old explosives in the area and in that moment, Koichiro hits an unexploded bomb with his shovel, causing an explosion that kills him instantly. His family and followers are left to watch in shock and horror and his blood, limbs and flesh rains onto them.
- The name Koichiro means "navigation/navigate, sail, cruise, fly" (航) (ko), "one" (一) (ichi) and "son" (郎) (ro).
- Koichiro's surname Mutoh means "military, martial" (武) (mu) and "wisteria" (藤) (toh).