Actor Allusion: Haruka's last name and mannerisms are modeled after Naomi Armitage from Armitage III, a role once taken by her Japanese voice actress, Ryoka Yuzuki.
The Danza: Mai Tokiha shares her voice actress's first name.
Fan Nickname: Sara Gallagher is nicknamed "Batman", for her black Robe that resembles Batman's outfit.
"Manshiro", for Manga!Mashiro for obvious reasons.
Name's the Same: Mashiro Blanc de Windblum. Don't confuse her with her Mai-HiME counterpart. They are nothing alike.
On the other hand, Mashiro Kazahana was an Older Than They Look semi-immortal reincarnation, so its possible that when the Hime incarnation was younger, they were more alike. In fact the Obsidian Prince remarks at one point "why are the masters of Kagutsuchi always so difficult?"
Role Ending Misdemeanor: As punishment for spoiling the ending to Mai-HiME, Tomokazu Seki's character, Yuuichi Tate, was written out of the Otome anime, reduced to a silhouette in one character's flashback (without any speaking parts).