In Vietnamese origin mythology, Lạc Long Quân is a dragon lord associated with the sea and water, while Âu Cơ is a fairy or immortal woman associated with the mountains. Their marriage is traditionally presented as the mythical origin of the Vietnamese people, joining the worlds of the dragon and the fairy, the sea and the mountains. According to the legend, Âu Cơ gave birth to a sac containing one hundred eggs, from which one hundred children were born. These children are regarded as the ancestors of the Vietnamese people.
The legend later states that Lạc Long Quân told Âu Cơ that they could not remain together because they belonged to different realms: he was descended from dragons, while she was descended from immortals. Lạc Long Quân therefore wished for the family to separate according to these two worlds. Following this wish, the children divided themselves into two groups: fifty followed Lạc Long Quân to the sea, and fifty followed Âu Cơ to the mountains. For the purposes of this debate, fighting to keep the Hundred Children together means that Âu Cơ resists this division and attempts to preserve the unity of the first family, instead of accepting their separation between mountain and sea.