を機に|をきに

Taking an event as an occasion or turning point to begin something new or make a change. The following clause usually describes a deliberate action or decision prompted by that event.

A somewhat formal expression used in writing, speeches and careful speech, often for life events such as illness, marriage, job changes or anniversaries. It marks the event as a chance someone seizes to act, rather than simply the cause of what follows. Compared with をきっかけに, it sounds more formal and more strongly suggests a deliberate fresh start.

• をきっかけにN2「をきっかけに」has essentially the same meaning and attaches the same way as 「を機に」, and the two are interchangeable in most cases. The difference is register: 「をきっかけに」is neutral and works in both speech and writing, while 「を機に」is more written-style and carries the nuance of 'seizing this opportunity.'
• を契機にN2「を契機に」is basically identical to 「を機に」in meaning and attachment, and they are interchangeable in most cases. 「を契機に」is stiffer and more solemn, common in news and speeches, whereas 「を機に」often carries the nuance of 'seizing this opportunity.'
• を皮切りにN1「を皮切りに」does not involve a turning point; it simply states where a series of things begins, and the following clause must imply successive occurrences or expanding scope. When someone starts a new action or changes as a turning point, use 「を機に」— the two are generally not interchangeable.
• てからというものN1「てからというもの」attaches to the て-form of a verb and stresses that a state has continued ever since, so the following clause cannot express volition; 「を機に」mostly attaches to nouns, and the following clause is often a decision made on that occasion. They are roughly interchangeable when describing ongoing change after that point.
• に際してN2「に際して」only marks the moment 'on the occasion of,' and the following clause is typically speeches, procedures, and the like. When an important event is accompanied by a new action, both can be used, but 「を機に」emphasizes the trigger and turning point. With verbs, 「に際して」takes only the dictionary form, not the た-form.

をきっかけに is broader and more casual, covering any trigger, even accidental ones. を契機に is stiffer and suits larger social changes, を皮切りに marks the first in a series of events, てからというもの (て形) stresses a lasting change ever since, and に際して simply means 'on the occasion of', describing what is done at that time without the turning-point sense of を機に.