The Nightingale is a tale written by Andersen concerning the contrast between natural and artificial beauty, in the aspects of music, splendour and above all else life.
The titular bird that sings before the Emperor of the story has various connotations in not just Danish whence Andersen in part wrote about it from, but also other countries.
The Japanese translations use uguisu (鶯 in traditional, older style and 鴬 in new styles of character), for the word describing the nocturnal singer, here - however - the word refers more precisely to Horornis diphone, the Japanese Bush Warbler, a bird of similar kinship to the Common Nightingale, Luscinia megarhynchos, whose symbolism is one of supernatural pleasure, beauty and revivification - the latter aspect being shared with the Japanese where the bird is an icon of Spring, and as such a word used in Haiku for vernal imagery - owing to its epithet harutsugedori (春告げ鳥, "Spring-calling bird").
The bird's Japanese name stems ultimately from the onomatopoeia ugui (うぐい). which is how the bird's call was described to sound like during the time that the Old Japanese language was spoken, there pronounced ugupisu.
Bathrobe's excellent website Sibuga offers plenty of insight into the birds' importance and biology in Asia, whence I have also done much research to whom I owe much gratitude, by all means visit it.
The Common Nightingale anciently appeared in Ovid's stories of Philomena, a young beauty whose final fate was that of being turned into the bird hence the adjective describing the bird is philomelian, relating to the Greek myth. Later poets such as Wordsworth and Poe have venerated the bird as a symbol of fatal and entrancing pulchritude - its song capable of whisking one into the state of wanting to die, and the bird itself, in Poe's story, impaling itself on a white rose to redden it in order that it may gain a transcendental end.
Thus, Andersen's choice of bird for this tale was steeped in European as well as Asian tradition - though the latter deals with a different if similar avian relation.
H. C. Andersen was mesmerised by the Swedish opera singer Jenny Lind, whose appellation was "the Swedish Nightingale" due to her sonorous voice and elegance. Andersen himself dedicated the story to her - though to merely call the fairy-tale an homage to Lind does the overall themes disservice in terms of overlooking plenty of more themes than just the beauty of singing and artistry.
As with Andersen's other stories, it contains several complex layers, one of the most poignant being how the mechanical Nightingale may be able to produce the same songs of the real life bird, but fails utterly at capturing the natural and spiritual beauty of it - something that the Emperor near the end of the story realises as he becomes mortally ill and wishes the song of the bird to soothe his suffering which the real bird in the end achieves, but also works as a harbinger of death. The latter owing much to its fatal entrancing qualities from myth and possibly that which, if we are to believe Mary Tartar - who translated and annotated Andersen's collected works - was the main source of inspiration for Edgar Alan Poe's own work.
The bird is not purely a harbinger of death as much as a manner of pscyhopomp - a guide of dead spirits - and one that wards off death with its numinous song.
Spring comes and goes, being the season of revival and new life - freeing plants and animals from the throttle of Winter. Hence, the Uguisu of Japanese culture is a herald of Spring and of new life, The deathly apparitions that haunt the Emperor during the end of the story are referred to in Japanese translation as shinigami, the equivalent of the grim-reaper, very much cementing how the Uguisu saves and soothes the Emperor during this moribund-induced nocturnal visitation.
Proving that even man-made imitations of nature fail to capture to the truly transcendent life of nature.