The tailed green-banded line-blue (Nacaduba cyanea) is a species of butterfly in the Lycaenidae family, and formerly considered a member of the genus Danis. It is found in the Indonesia (Irian Jaya, Maluku), Papua New Guinea, the Solomon Islands and Australia (Queensland). The wingspan is about 30 mm. Adult males are blue with a dark brown wing margin. There is a pale blue to white patch on the hindwing. Females are white with a broad black border and a row of blue edged black spots.