kitsune-me キツネ目

In Japanese, kitsune-me キツネ目, "fox eyes," are narrow, upturned eyes, like those of a fox. In anime, characters with fox eyes are normally drawn with them closed, so they end up being a mix of ito-me 糸目 and tsuri-me ツリ目.

It's also spelled kitsune-me 狐目.

Character: Ichimaru Gin 市丸ギン
Anime: Bleach (Episode 22)

Examples

In principle, fox eyes should look like a fox's eyes.

Character: Tenko Kuugen 天狐空幻
Anime: Wagaya no Oinari-sama. 我が家のお稲荷さま。 (Episode 1)

That is, they're upturned, narrow and long.

kirenaga
切れ長
Long. (eye-shape.)

In anime, characters with fox eyes tend to have them closed all the time. They don't have to be closed to be fox eyes, but they're usually closed.

Characters with fox eyes tend to be mischievous or scheming like foxes. In particular, the fox eyes give the impression the character is evil or has ulterior motives.