Cao Cao Sisters/Relationships

Reki
Reki is the Cao Cao sisters arch-nemesis, especially Juju due to being snipers. The sisters (Juju, Paoyang, and Meimei) tried to have Reki and Kinji killed in an ambush sniper attack, which almost killed Reki. Then, during the train hijack, the sisters tried to have Reki commit suicide until it was thwarted by Kinji and Reki help defeat the sisters.

Riko Mine
Meimei taught Riko while part of IU how to make and use explosives, especially in hijackings as shown in Volume 1. The Cao Cao sisters placed a switch for a bomb under Riko's seat during the train hijacking to prevent her from helping Kinji and Aria.

Kou
The Cao Cao sisters treat Kou similar to the way Aria treats Kinji by having her run errands for them due to her having a timid personality that can be taken advantage of.

Sun Wukong
The Cao Cao sisters appear to work well with Sun as shown when they teamed up to fight Team Baskerville in Hong Kong as well as their dislike of their superior Shokatsu.

Seigen Shokatsu
Shokatsu is the Cao Cao sister superior officer in Ranpan who they despise possibly due to their ancestor being defeated by Shokatsu ancestor.