Moeka Kiryuu

A tall girl that Rintarou bumps into in Akihabara and is on a search for the IBN 5100 personal computer. Moeka is extremely protective of her mobile phone and becomes agitated if someone tries to take it from her hands. She is very shy and prefers to talk to someone by sending them a text message instead of speaking.

In Episode 12 it is revealed that she's in fact a Rounder member, a unit belonging to SERN. Her codename is M4. In multiple timelines of the Alpha attractor field, she is the one who kills Mayuri.