Moeka Kiryuu (桐生萌郁, Kiryū Moeka) is a tall girl that Rintarō bumps into in Akihabara. She is on a search for the IBN 5100 personal computer.
Moeka is extremely shy, her preferred form of comunication being via text messaging even if the person she is "talking" to is right in front of her. As such, she is very protective of her phone and becomes agitated if someone tries to take it from her hands. Amusingly though, her messages are very lively, often using stars, hearts and musical symbols to convey an upbeat feeling.
Moeka seemed more or less interested in Rintarou, calling him Okabe-kun, and constantly sends him emails as attempts to talk to him, though this is unclear if she wants his company or simply because she has been ordered to. Her habit of constantly spamming his mailbox with lengthy SMS's made Rintarou ignored them, much to her dismay.
In one of the drama CDs, Moeka narrates a message she sent and sounds like a completely different person.
Moeka can apparently type and send SMS's at the speed of normal speech, which leads to Rintarou calling her "Shining Finger" (Masseuse in the game).
Moeka fell into a deep depression for an unknown reason and decided to kill herself. At that moment she received a mail from the enigmatic FB, changing her life forever. Seeing FB as the person that gave her life meaning, Moeka devoted every waking moment to carrying out her given orders, developing a dependancy on FB and the mails provided. While she is capable of carrying out atrocities for acceptance, Moeka strives to be loved and has the potential to be a good person if led in the right direction.
Her blind devotion to FB is fruitless, however, as she was considered no more than a pawn on SERN's board and are "expendable".
Rintarou first encounters Moeka around the RadioKaikan building when he was revisiting the "satellite crash site". Moeka took a few pictures of him, which irritates him and he orders her to stop, though she persists. Rintarou then offered to exchange emails under the condition that she stops. She immediately began sending him text messages before leaving. Moeka was apparently a reporter, according to her introduction.
After floods of text messages, Moeka visits Rintarou's lab and demands to see the IBN 5100 (as she was the one who suggested it to him). Without asking, she attempted to carry the computer away (before crumbling under the box's weight). Rintarou reluctantly dubs her "Lab Member 005" to prevent her from leaking the IBN's secret. She does not do much beyond this point.
After the Future Gadget Lab have perfected the time-leaping mechanism, a team of Rounders, led by Moeka storms the lab and holds its members at gunpoint. She ordered them to hand over the IBN, while shooting and killing Mayuri Shiina for being "unnecessary", causing Rintarou to panic. She points her gun at him and prepares to shoot, but Suzuha Amane rushes in and takes out the whole Rounders squad, giving Rintarou his chance to time-leap back in time to prevent the attack.
Rintarou tracked her down and attempted to force her to abandon her assault, but was captured by her Rounders. The group then proceeds to breach into the lab and kills Mayuri, again, prompting Rintarou to leap into the past.
Moeka continues to kill Mayuri again and again in Rintarou's various plans to save her.
A few days into the past, Rintarou comes to her house to revert her D-mail and convince her to cancel the attack, only to find her dead in her apartment, having hung herself. He time-leaps again, and returns to her house. Moeka seemed catatonic, mumbling to herself while typing uncontrollably. She told Rintarou the story of FB and the person's significance in her life, and that FB have ceased all communications with her. Rintarou attempted to wrest the phone from her hand, causing her to violently revolt. He succesfully sends a D-mail to the past, but nothing changes (as the phone Moeka convinced her past self to change did not appear), thus pointing Rintarou's attention towards FB. He and Moeka then tracks FB down, who turned out to be Rintatou's landlord, Yuugo Tennouji. Yuugo kills himself after revealing the truth to the two. His daughter Nae witnessed this and stabs Moeka in the chest, killing her.
In the anime, Moeka was shot and killed by Yuugo instead.
Moeka is not seen or heard of anymore after her death. After 1% divergence was reached (true ending), Moeka can be seen at the CRT shop, working for Yuugo as an employee.
- Moeka has her own route in the new visual novel, Steins;Gate: Hiyoku Renri no Darling, which even further displays her interest in Rintarou.