I'm Japanese. There're many word for death like "shi" "shi-bou" "saigo" "shu-en" "shinigami"and more. FYI, "aenaisaigo" nicely fits for death but it is a phrase not a word and it can be translated as "never see again".
Colloquial for death in Japanese in some area like Hiroshima, Shimono-seki, Miyoshi, is, "Santa Maria". I was surprised myself when my Japanese friends said it when.