Who is the short hair girl? Who is "Koko" or is this something we learn later? Rereading and can't find her mentioned before even though his sister was, so I'm confused
I don’t think there’s too much to read into atm. She was identified as “Koko” because she yelled it out as part of the name for her attack. I’m sure there will be cause to care more about her in the future (if current developments are any indication), but for now her only point of intrigue is that she’s yet another humanoid shuuki.