Kobato Hasegawa

Kobato is a shy person that doesn't tend to interact with the strangers around her. She is extremely close to Oni-chan, and gets jealous if he diverts his attention from her. 

During her 7th grade, Kobato saw second season of anime "Kurogane no Necromancer" and after that has developed obsession with it. She has had a penchant for darkness, vampires and the macabre ever since.

As a result she often speaks in an affected fashion, claims to be known as the ancient vampire "Reisys VI Felicity Sumeragi", and wears a Gothic dress and a red contact, but this facade quickly breaks down when she gets emotionally worked up and she speaks in a strong Kyūshū accent.

Indeed, her behavior does not for the most part differ from that of a regular girl (procrastinating with her homework, staying inside when it is hot, etc.) which Oni-chan  points out, causing her to be embarrassed and slightly lose character.

Kobato has a rather serious brother complex, as she gets angry when someone else, females in particular, gets too close to her Big Brother, which she calls Oni-chan.