Hotaru, an only child, is very shy and isolated. She doesn't make friends easily. In fact, she scares most would-be friends off b/c she has a strange power: she can heal wounds. Her classmates claim that this odd ability of hers is unnatural and gross. This has led to her spending most of her time alone in her father's mansion. Her mother is dead, and her father does not have much time for her; he is always off with his experiments...
Hotaru, herself has a very weak body; she can exhaust herself much quicker than any normal person. This seems to work, at least partly, as a tradeoff for her ability to heal. She needs a friend that will love her no matter what; a friend who will never leave her. I believe a cabbit would be the perfect companion for Hotaru.
Cabbits are adorable little creature: half cat, half rabbit. They are intelligent and loyal, and very low maintenance. ^_~ All you need to do is love them and feed them carrots. A cabbit would do its best to make Hotaru happy. If Hotaru was to grow faint or pass-out, (as she sometimes does) the cabbit could fly her home. No matter what, a cabbit would stay by her side, and that is the kind of friendship she needs.