During her first appearance in Silent Sinner in Blue chapters 1-2, this rabbit who would later be given the name Reisen wore a dress very similar to Tewi Inaba's, probably because she wanted to disguise herself as an Earth rabbit.
"Reisen" is in fact not her true name, but is the name she received when she became the Watatsuki sisters' pet. No one knows her real name as of yet.
The color pages of SSiB chapter 15 depict the rabbit shown at right who has short light blue hair and red eyes. This may possibly be Reisen II, or else it could be one of the other Lunar Defense Corps rabbits. Note that her ears are straight instead of being flopped over like Reisen's, but they may have been raised in surprise. Most fan artists assume that this rabbit is indeed Reisen, and use these hair and eye colors for her in their art.