便
biàn · HSK 6
soon afterwards
便 = 亻(person) + 更 (change/again); a person who acts conveniently/promptly
便 means convenient or then/soon. Decomposition: 亻 (person radical) + 更 (gēng, to change). A person who adapts quickly does things conveniently and right away, hence as early as or soon afterwards.
便 — person 亻 + change 更
A semantic compound: 亻(person) beside 更 (to change/replace). The original sense was a person making things easier or more convenient by adjusting them. From 'convenient' it extended to 'then/thereupon' (biàn) and to bodily 'discharge' (as in 大便).