主任
しゅにん · shunin · JLPT N1 · noun
mission
主 — flame/lamp on top of a stand 王
Originally a pictograph of a lamp with a flame on top of its stand, representing the lord or master of the household who tended the fire. The meaning extended from 'lamp/host' to 'master, owner, main, principal'. The character 炷 (wick) preserves the original 'lamp' sense.
任 — person radical 亻 + 壬 (phonetic)
任 combines the person radical 亻 with 壬, which supplies the sound. The original sense centered on a person bearing a load or burden, which extended naturally to 'carrying responsibility,' 'duty,' and 'to appoint someone to a post.' Modern uses like 任务 (task) and 责任 (responsibility) preserve this core idea.