So the latest Blue Archive Livestream revealed their 2nd crossover collaboration (the 1st being Hatsune Miku) will be A Certain Scientific Railgun. However, only three Railgun characters will appear in Blue Archive; Mikoto, Misaki and Saten. Hence this picture where Kuroko doesn't get to be with her "Onee-sama" in this collaboration.

Edit:Also, Shiroko Terror's nickname by fans is "Kuroko" hence why she's with Railgun's Kuroko.

Guess what? What was once a Japan-only collab six months ago has just popped up elsewhere; Mikoto and co are now in the English version (and in the Korean one at least).