Vaso-occlusive device and delivery assembly

A vaso-occlusive treatment system includes a delivery assembly; and a vaso-occlusive device detachably coupled to the delivery assembly by a delivery assembly junction. The vaso-occlusive device includes a braided portion formed out of one or more composite wires, a coiled portion coupled to the braided portion, and an intra-device junction coupling the braided portion to the coiled portion. Each composite wire includes a core made from a core metallic material, and an external layer made from an external metallic material different from the core metallic material. One of the core and the external layer has a greater radiopacity and a lesser stiffness, respectively, than the other one of the core and the external layer.