He leads the unit as a sergeant.
Standard kanji spelling for this JGSDF rank abbreviation.
Numerical variant using full-width digit ３; less common but attested.
Abbreviation of 三等陸曹 (santō rikusō), literally 'third-class land sergeant'. The kanji 三 means 'three', and 曹 is a historical term for a non-commissioned officer or official.