改まる
あらたまる · aratamaru · JLPT N1 · verb-godan
to be formal
改 (change) + まる (become): to become changed, i.e. renewed or made new; the same kanji-like shift gives 'formal' as a reset to proper form.
改 means change or revise, and まる marks a state becoming. Renewal and formality share this idea: a new start or a proper, reset form.
改 — 己 (self) + 攴/攵 (action/strike)
改 is a compound of 己 'self' and 攵 (the action radical, originally a hand holding a stick). The image is of striking or applying force to oneself or one's situation, suggesting reform or correction. From this came the modern meaning 'to change, alter, correct'.