I do not understand how demon diary can be classified as shounen ai.
is it because renelf looks like a girl?
there is absolute no mention of anything close to romance in this story, except for Erutis and Krayon. which is not gay.

if demon diary is a shounen ai, then so should Black Butler.
and it clearly isn't

It's not so much the romance, but the "hints".
I'd classify this one as slight (very slight) shounen-ai; the hints are obviously there (implied more than once) but it never goes beyond that.

I'm pretty sure people there would be more people complaining if it weren't classified as shounen-ai. O_O

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Monkeys, always at your service.

It's shounen-ai only in the dreams of many a fangirl, and in the eyes of those that are rabidly anti-shounen-ai/yaoi.

Personally, I don't think it is shounen-ai. As you said, there's no m/m romance (or really any romance) involved in the story. But since BU is edited by users, somebody obviously thought it was s-ai.

There are many instances of this. Maybe we need a "bishounen" category?

It is not really a shonen-ai, it only very subtly hints at it. But it really depends on your own opinion you can interpret it as a mild shonen-ai or just a story of friendship

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As far as I'm concerned, Black Butler IS honorary shounen ai.

Just kidding! I think I just love the subtext... and it's put in there deliberately so ppl can't be blamed for thinking it's shounen ai if they want to.

I think it's the same with Demon Diary.