 If you liked
+C: Sword and Cornett
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 ...then you might like
Sable Prince
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While the plot and storytelling-ways differ quite a bit, both these manga give off similar feelings.
Along with the beautifully detailed art, a few disturbing themes are mixed in, and a great scale conspiracy seems to lure around the corners.
But, even so, neither are excessively dark stories, triving more on lighthearted humor and fleshing out the characters.
Also, both stories feature a prince and his sidekick on an adventurous quest, even if that's really all the main characters share.
It's not certain, but I'd say there's a high probability that if you liked one, you'd like the other, too.