Gemstone Girl

As the nick name implies, she is a Gemstone who's name has been unrevealed and who's power hasn't been detailed. She debuted in Volume Toaru Majutsu no Index Light Novel Volume SS2.

Chronology
Her biggest distinctive features are that she walks around with a suitcase handcuffed to her right hand, her young looks which imply that she should be around her late teens and that she wears a one piece dress that has been described as "covering so little, that isn't much of a clothing". It should be noted that she is unusually beautiful for someone of her age, gifted with a gorgeous face and a feminine body line.

She meets Kamijou Touya in a train station while she was lost; in a very Kamijou way Touya selflessly approached her without her requesting any help gave her proper instructions on where to go and after which they parted ways. Later she will appear in a bar where Misaka Tabikake and Kamijou Touya had just became acquaintances, at that point she is making a run from her pursuers. As soon as Touya sniffed trouble he made a run out of the place at Match speed, however the Gemstone girl was running right behind him.

The pursuers followed them with such resilience, that Touya, the gemstone girl and Touya's kouhai needed to fake their deaths in a plane crash in order to shake them off.

Abilities
While not detailed, her ability seems to be related to sound. She once used a strong noise to knock down several people.

Quotes
(Volume SS2) : "Patrons of this bar that has become an area of danger,” --- “I seem to have gotten you involved in a worrisome problem, but do not fear. I will ensure that you survive.”

Trivia

 * Misaka Tabikake dad could recognize at first glance that she was a gemstone.
 * She seemed to have become slightly attached to Kamijou Touya, not only she followed him from her own initiative, but in the cover of the light novel volume she is seen holding his suit while he is getting away. This attachment might have come from Touya's unexpected act of kindness towards her when they first met.