Chikage Kushinada: It is not known what her exact relationship is to her other than that she is her master but she treats Chikage better than the other members in yomi (other than Sho Kano). Sometimes thier relationship can seem a bit estranged, and their are times when Mikumo wants to break her into a heartless killing machine, but on the other hand seems to be proud of her like a parental figure and is willing to give Chikage room to develop on her own watching from afar with a neutral expression. However after Chikage had a breakdown out of an innerconflict over killing her friends, Mikumo took the first action towards interfering, and knocked her out and took her away for more training. She now blames Kenichi for this turn of development and asked Freya to tell him to stay away from her disciple.
Sho Kano: It is unknown what their relationship was though his death did not seem to affect her much, and she even disregarded him after his death. This implies that their relationship was not very positive, or atleast not as positive as it could be.
Rachel Stanley: After her master's defeat, Mikumo told her that their defeat was the fault of her master. It is unlikely that Mikumo made the attempt to take her life as she knocked her out instead and later aided in Rachel recovery and protected her from other members of YAMI.