User blog comment:B214/Light Novel Volume 16 spoilers/@comment-9339850-20131019082251/@comment-1359322-20131019085742

At this point where Issei is facing strong opponents, i'm wishing for perhaps an Alchemist or something that can give Issei a means to fight without the Boosted Gear. But i've no problem with Le Fay being Issei's magician.

BTW Vali being Odin's adopted son isn't official yet, so Le Fay is still a terrorist. Until Volume 17 that is.