We won't do it.
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Updated by a moderator
Posted under General
An alias wouldn't have worked out anyway, since 12 other tags have Otonashi as a last name.
But because of those 12 other tags, something ought to be done. Plot-irrelevant spoiler or not, Otonashi Yuzuru does look a lot better than Otonashi (Angel Beats!)... But then, the same could be said about Tenshi (forum #41467), and that was a no, too.
Add the AB qualifier?
I actually don't see the big deal with this one as a spoiler, but it's probably better to stay consistent with all the other *_(angel_beats!) character tags. Aliasing those two names to their respective qualified tags wouldn't be a bad idea either, at least until the show is finished airing and the issue can be looked over more objectively.
Is it really that uncommon for a character's full name to not be revealed until later? Tenshi you could sort of build a case for (even though the first words out of her mouth are "I'm not an angel"), but girl_who_sits_next_to_yui_(k-on!) --> tachibana_himeko has as much plot relevance as this one.