〜際（に）
On the occasion of 〜際（に）
Meaning
A formal "when ~", "on the occasion of ~".
Formation
[verb dictionary / た form] + 際（に） · [noun] の + 際（に）
Notes
The stiff cousin of 〜とき, reserved for occasions that matter — applying, boarding, an emergency. It does not fit trivial daily actions: ご飯を食べる際 sounds absurd. 〜際は is the standard opening for public warnings and instructions.
Examples
帰国（きこく）する際（さい）に、先生（せんせい）にあいさつをしました。
I said goodbye to my teacher when I returned to my country.
Breakdown
お降（ふ）りの際（さい）は、足元（あしもと）にご注意（ちゅうい）ください。
Please watch your step when getting off. (a standard announcement)
Breakdown
申し込（もうしこ）みの際（さい）に、身分証明書（みぶんしょうめいしょ）が必要（ひつよう）です。
Identification is required when you apply.
Breakdown
面接（めんせつ）の際（さい）には、この書類（しょるい）をお持（も）ちください。
Please bring this document to the interview.
Breakdown
非常（ひじょう）の際（さい）は、このボタンを押（お）してください。
In an emergency, press this button.
Breakdown
⚠️ Often confused with
〜た後で / 〜後
After doing 〜後で
"After doing ~". Attach to the ta-form of a verb, or a noun + の. Note the contrast with...
〜てから
After doing (and then) 〜てから
"After doing ~ (and only then ~)". Emphasizes that action B happens AFTER action A is comp...
〜前に
Before doing 〜前に
"Before doing ~". Attach to the dictionary form of a verb or a noun + の. The action AFTER...
〜たとたん（に）
The moment 〜たとたん
"The moment ~", "just as ~" — the second event follows instantly and unexpectedly.
〜次第
As soon as 〜次第
"As soon as ~", "the moment ~ is done". Formal, and always about the future.
〜以来
Ever since 〜以来
"Ever since ~" — a state that has held continuously from a past point until now.
〜たびに
Every time 〜たびに
"Every time ~", "whenever ~" — the second thing happens on each occasion of the first.
〜ぶり
After an interval 〜ぶり
"After an interval of ~" — how long it has been since this last happened.
〜かと思うと
No sooner than 〜かと思うと
"No sooner had ~ than ~", "just when you think ~" — two events tread on each other.
〜上で
After (formal) 〜上で
"After ~ing (and on that basis)" — a deliberate step taken before deciding.
〜ところに / 〜ところへ
Just as / right when 〜ところに
"Just as ~", "right when ~" — something arrives at exactly that moment.
〜に際して
At the time of 〜に際して
Formal "on the occasion of ~", "at the time of ~" — used as something significant begins.
〜てはじめて
Only after 〜てはじめて
"Only after ~", "not until ~ did I …".
〜てからというもの
Ever since then 〜てからというもの
"Ever since ~" — a turning point after which things have stayed changed.
〜に先立って
Prior to 〜に先立って
"Prior to ~", "in advance of ~" — a preliminary step before a major event.
〜が早いか
The instant that 〜が早いか
"The instant ~ happened, ...", "no sooner ~ than ...".
〜や否や
Scarcely when 〜や否や
"As soon as ~", "scarcely had ~ when ..." — the two events are almost simultaneous.
〜そばから
No sooner done than undone 〜そばから
"No sooner is ~ done than (it is undone)" — the effort is immediately cancelled out.
〜なり
Immediately upon 〜なり
"The moment ~", "immediately upon ~ing" — one action leads straight into an unexpected nex...
〜を境に
Marking the turning point 〜を境に
"With ~ as the dividing line", "ever since ~" — a clear before and after.
〜がてら
While also doing 〜がてら
"While ~ing", "taking the opportunity of ~ing to also ..." — two purposes in one outing.
〜間際に
On the verge of 〜間際に
"Just as ~ is about to happen", "at the very last moment before ~".