For once, i like to see the main characters with slanted eyes as their main features. It's kinda difficult since those with fox-eyes tend to act as the antagonist in most genres. The only one i can think of is Naruto, since he occasionally go into fox-eyed mode throughout the series.

Even though these are not the main characters, examples like Gin Ichimaru from Bleach, and Kitsune from Love Hina.

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The protagonist of Takemitsu-Zamurai has fox-eyes. Of course it had a rather strange art style so you may have a hard time getting into it.

Xellos from Slayers maybe if you meant with the second part that you're ok also with not main characters.
Anyway he's quite one of the main chars in Slayers Try anime.

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What I like in Trivial Pursuit style. Pick your category:

sayonara zetsubo sensei XD

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Limits are there to be ignored and be broken eventually by someone else
-Kyon, Live A Live, The Wavering of Suzumiya Haruhi

in today's world, if you're not moe, you can't get a decent job
~Harunobu Madarame, Genshiken

The main dude in From Far Away has slanted eyes.

Sho in Akumetsu has them as well. (Not at first, but he develops them)

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Ookami to Koushinryou

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