Chrome Shelled Regios: Missing MailChrome Shelled Regios - Missing Mail; Chrome Shelled Regios: Missing Mail; Koukaku no Regios: Missing Mail; 鋼殻のレギオスＭＩＳＳＩＮＧ　ＭＡＩＬ; 鋼殼都市雷吉歐斯; 钢壳的雷吉奥斯

In this school fantasy story set in the distant future, mighty creatures known as filth monsters have overtaken the polluted land, forcing humanity to live in isolated mobile cities called Regios. One such city named Zuellni is a self-sufficient Academy City in which freshman Layfon Alseif has just enrolled. Layfon reluctantly joins the 17th Platoon led by the third-year student Nina Antalk and embarks on a series of adventures. This version recounts a slightly different version of Layfon's story.