Tatsugami Otohime

Tatsugami Otohime (竜神 乙姫) is Kamijou Touma's cousin and is shown in the Angel Fall Arc. She does not show up again after the Angel Fall incident, in neither the novels or the 1st season of the Index anime. She has more screen time and thus is slightly portrayed better in the novels.

Personality
Her personality is playful and enjoys acting childish, she has stated that hugging Touma, clinging to Touma or flirtling with Touma (in public or private) is completely ok. She prefers to calls Touma Onii-chan. Kamijou Shiina mentioned that they were pretty close and that they shared a bed on an afternoon nap once.

The Angel Fall incident changed her outer appearance with Tokiwadai's Ace Railgun Mikoto, a fact that greatly disturbed Touma in more than one opportunity. He described her behavior as that of a "little sister type" character.

Chronology

 * Main article: Angel Fall Arc

Trivia

 * Her design was created for the Anime.
 * Kamijou's mother supposed that Otohime and Touma haven't met since kinder garden since he hasn't gone to his uncle house since then, however Otohime's cellphone pic proves otherwise.
 * Since Otohime's real body was never seen in the anime outside a picture we have that "her real voice" was never heard, and thus all of her lines were voiced by Rina Satou while Otohime was in Mikoto's body.

Quotes

 * (To Touma) "What, Oniichan? Are you still mad about earlier? It doesn't matter, does it? Whether I hug you, cling to you, or flirt with you?"
 * (To Touma) "ONNIIIIIIII--CHAN!! THE ALARM-CLOCK-REPLACEMENT-ATTACK IS HERE!"