I was trying to update the Sen no Kiseki wikis with search tags for pixiv, and for some reason, I am unable to add:
閃の軌跡Ⅱ
閃の軌跡Ⅲ
and 閃の軌跡Ⅳ
...with the funny single-character roman numerals. These actually seem to have more hits than the individual characters equiv., so I'm not sure if the site is interpeting the Ⅳ as IV etc. in which case it really shouldn't be.
*edit*
黎の軌跡Ⅱ as well.
Updated