Chūji Shimizu is the Chief Petty Officer aboard the Blue Noah warship, commanding the submarine Shīra. This key auxiliary vessel undertakes independent missions critical to the war effort. Shimizu directly trains and integrates young survivors into the crew, developing their skills and discipline as operational team members. His leadership encompasses tactical combat operations, including coordinated assaults on vital alien installations like the Gravity Control bases at Earth's poles. During the crucial mission to destroy the North Pole base, he commanded the submarine Tempest Jr., confronting overwhelming resistance; the mission ultimately failed, leading to strategic setbacks. Following Blue Noah's upgrade into a space-capable vessel at the N9 facility, Shimizu continued to lead the Shīra. In the final offensive against the alien forces, he operated jointly alongside two additional support ships. He consistently operates within the established chain of command, maintaining a professional relationship with Blue Noah's senior officers during both undersea and space combat scenarios.