OK, the booklet and just about any website I've seen credit this song as Artist: hitomi and Composer: 黒石ひとみ (Kuroishi Hitomi). (here's a link: http://joshinweb.jp/dp/4988002515943.html). Though according to Wikipedia, this Hitomi's surname is Furuya. Could be that this hitomi is simply performing for this other Kuroishi Hitomi person. So yeah, I don't know what's the real tag and I don't know if the "hitomi" of this song is the same Hitomi of this Last.fm page. Help.
Yup, I can see it both ways, as dotTomi said. I think I've seen it credited as Hitomi in the booklet or somewhere and iTunes Gracenote credits Stories to 黒石ひとみ. (Of course, iTunes is the one who messed up the Lucky Star voice actresses' kanji tags =P)
Her vocal performances are credited as Hitomi in the booklet. Boo hoo sorry this clashes with your idol, but this is the correct tag. Until artist moderation is reinstated, live with it. I'm coping just fine.