KanjiJLPT N3
Occasion

occasion, side, edge, verge, dangerous, adventurous, indecent, time, when

Mnemonic

At the edge of the village, a ritual marks the boundary between the known world and the wild beyond. This occasion happens only when two realms nearly touch — a juncture so rare the entire village gathers to witness it.
Additional thoughts
Picture the village perched on a border. The ritual is performed at the exact point where two territories meet — that's the occasion: a rare boundary moment. Village edge + ritual ceremony = a significant occasion at a juncture.
Quick recall
A village ritual at the boundary marks the rare occasion when two worlds meet.

Details

The keyword for 際 is occasion. This kanji refers to a specific time, moment, or circumstance when something happens, as in "on the occasion of" a particular event. It also carries the meaning of a boundary, edge, or juncture where two things meet, suggesting the point at which one situation transitions into another. By extension, it is used in contexts relating to international or inter- relationships, where different entities come into contact at their borders or boundaries.
On'yomi
さい
Kun'yomi
きわ、-ぎわ