際
さい · sai · JLPT N3 · noun
on the occasion of
際 = 阝 wall + 祭 festival: the edge where things meet, the moment
阝 is a wall or mound and 祭 (sai) gives the sound. It first meant the seam where two walls meet, then any edge or moment, so ~の際 means on the occasion of. It also appears in 国際 (kokusai, international) and 実際 (jissai, actually).