Boob Window (Hole on Chest Revealing Cleavage) - Examples, Term in Japanese

In anime, when a girl's clothes for some reason has a hole in the middle of the chest that lets show her breasts, the term for that in Japanese is tanima hooru 谷間ホール, literally "cleavage hole." In English, it's usually called "cleavage window," or "boob window."

A single word term for it is "keyhole." Sometimes, it's also called a "peekaboo."

Kanroji Mitsuri 甘露寺蜜璃, example of "cleavage window," tanima hooru 谷間ホール.

Character: Kanroji Mitsuri 甘露寺蜜璃
Anime: Kimetsu no Yaiba 鬼滅の刃 (Episode 22, After-Credits Scene)

Examples

For reference, some examples:

Pirotessa ピロテース, example of "dark elf," daaku erufu ダークエルフ.

Character: Pirotessa ピロテース
Anime: Lodoss-tou Senki, ロードス島戦記 (Episode 9)

Context: a dark elf, daaku erufu ダークエルフ.
erufu-mimi
エルフ耳
Elf ears.

China Dress

One type of clothing that often features a cleavage hole is a "china dress," in Japanese: chaina-doresu チャイナドレス, whose technical name in English is "cheongsam," from the Chinese word chángshān 長衫.^{(en.wiktionary.org:長衫)}