User blog comment:B214/Volume 21 info & spoilers/@comment-50.139.232.230-20160204155647/@comment-26345952-20160205003735

Bikou and Arthur I doubt it; Kuroka or Le Fay, most likely since they are close to vali. But honestly I think that it will be someone of the main harem

BUT I STILL VOTE FOR KUROKA ON THE COVER.