Takitsubo Rikou

Takitsubo Rikou (滝壺 理后) is a member of ITEM. She later leaves the group along with Hamazura Shiage, after she becomes extremely weak due to abusing an ability-enhancing drug.

Personality
Rikou's personality resembles that of Aisa, in that she is rather blunt and rarely expresses her inner-thoughts. Despite the fact that she shows little emotion, she does care about her fellow 'ITEM' members and in particular, Shiage, whom she is in love with. Even with her friends she would normally behave quite coldy and detachedly but not in a bad way, she has been described as "lethargic" instead of stern or aloof.

Whenever a character has been put in a ridiculous position she usually address him / her with encouraging lines such as "Don't worry. It's ok, I'll support you", though her courtesy condescendence will probably have the opposite effect and would bring a heavy blow to whoever she was trying to cheer up.

Plot
Chronologically, she first appears in Toaru Kagaku no Railgun with the rest of ITEM in order to stop Mikoto from destroying a research facility. She helps Mugino hunt down their target only to become weakened due to the use of the drug, Body Clear.

In her fight against Kakine Teitoku in vol.15, she tries to manipulate his AIM field and use it in the form of an attack against him, forcibly attempting to make him lose control of his power and go berserk. This fails however, and due to her condition and the difference in their power, she still loses.

After leaving ITEM, she arrives in Russia with Hamazura Shiage after they hijack a jet from Academy City in District 23. Later, her condition becomes worse and she is handed over to a doctor only to find out that she can't be healed with the current technology in Russia. Shiage then tries to hide her whilst fighting against pirates alongside a villager and a soldier.

In the epilogue of volume 22 it was revealed to Shiage, Rikou and Mugino that Rikou is a very valuable test subject who has the potential to be the 8th person to reach level 5. Even more important is that since her power affects ‘Personal Reality’, it is teorized that Rikou's ability has an incredible potential; such as changing a person’s level or giving a person multiple skills. To put it simply, it would be possible to give Hamazura Shiage the Railgun’s power, or Mugino Shizuri can be demoted down to a Level 0. For this reason Rikou was to be retrieved alive while Shiage was not.

After volume 22 she becomes part of the new team "ITEM", which is composed of Shiage, Mugino, Saiai and herself, she has recovered to the point where her health is outside danger as long as she doesn't use Body Clear, thus she is unable of using her ability.

Abilities
Rikou's ability is AIM Stalker (能力追跡), which she uses to track down other espers. To use this power she needs to consume what is known as BodyClear, and in recent chapters, continued use of the drug has worn her body down to the point where she will collapse and become seriously un-well if she uses it again. Rikou developed in such a way that she can only use her ability by consuming this drug, as part of an earlier project to create a Level 6 before the 'Experiment' involving Accelerator, and thus she can no longer develop through the normal methods other espers go through.

She states that her ability allows her to steal other espers' abilities by memorizing their AIM field, potentially allowing her to become the eighth Level 5 esper in Academy City. This fact is also mockingly mentioned by Kakine Teitoku after their fight, who states what a shame it is that she has to rely on a drug to use her powers. She later suffers from brain damage after fighting him in volume 15; and as a result, she can no longer use her esper abilities.

Time after time it has been stated that Rikou can not use AIM Stalker without the help of a catalyzer such as body clear; however in the epilogue of volume 22 she manages to use her ability to help Mugino's aim with Meltdowner and in turn that move was used to save Shiage's life. So it might not be wrong to think that Takitsubo may be able to obtain some sort of level of command over her ability without Body Clear with enough hard work, but it just unknown just how much she will be able to do so.

Trivia

 * It is uncertain if Body Clear- the drug she uses to power her abilities- is a by-product of Telestina Kihara's research. However, both Body Clear and Crystallized Esper Essence seem to have the same effect on the user.