Writing systems extend even to fiction— famously so! In fact, creating a writing system is some of the most fun a linguist can have. Many hobbyists spend lots of time creating languages (conlangs) and coming up with writing systems that fit such machinations. Perhaps the most famous example of this would be the languages featured in The Lord of the Rings, written by J. R. R. Tolkien.
Tengwar, an alphabet Tolkien came up with, is a good example of a constructed writing system. Perhaps best known for being used to inscribe a pivotal plot element (the One Ring) in his novels, tengwar has an entire fictional history attached to it.
A bit of trivia: Tolkien was a linguist of the historical variety, more specifically a philologist— that is, he studied language in historical sources. Philology is a kind of ancestor to a specific subset of modern linguistics, similar to how “natural philosophy,” studied by the likes of Aristotle and Plato, was a precursor to modern natural science.
The creation of orthographies for constructed languages can be a creative outlet for many, and an interesting puzzle or thought experiment at the same time. Some methods of communication present unique challenges for writers and readers.