Tamaki acquires a little sister when Kirimi Nekozawa comes to Host Club looking for her older brother. Her true brother, however, is Umehito Nekozawa, president of The Black Magic Club. Sadly, while these siblings long to know each other, Umehito is light-sensitive and must forever live enwrapped in darkness while Kirimi is deathly afraid of both darkness and cats (but loves erotic literature). Tamaki makes it Host Club's duty to bring these siblings together - and who better to pull off a transformation to bring Umehito out of the darkness than Renge (even though Haruhi warns that their over-the-top efforts are only making things worse).
—statmanjeff