Simplified form of 鵼

It is an analogy-based simplified form of the rare character 鵼.

It keeps the left component 空 and writes the traditional right-hand bird component 鳥 with its simplified Chinese form 鸟.

How did the Japanese nue story develop?

The word began as a bird name, then gathered a monster story.

In the early Japanese chronicle Kojiki (712), a poem names a calling bird nue. It writes that sound as 奴延, two characters used for their sounds, rather than as 鵼.

In the early 13th century, the Japanese war tale The Tale of the Heike tells of a strange creature at court whose cry resembles the bird; accounts give its body different animal parts. Around 1724, a Japanese essay uses nue figuratively for a person or thing whose identity is hard to pin down. These are Japanese readings and stories attached to 鵼, not a reading shared by every language.