One popular title is 'The Time Machine' by H.G. Wells. It's a classic that explores time travel in a really interesting way. Another is 'Frankenstein' which can be considered a precursor to science fiction. It deals with themes like creation and the consequences of playing God.
You can try websites like Project Gutenberg. It offers a large collection of free e - books, including many science fiction works. Some of them are classic science fiction novels that are in the public domain.
I'm not very familiar with 'chisa x pon', so I can't say for sure if it's popular. There are so many manga out there that it's hard to keep track of all of them. It could be really popular within a certain niche group though.
The Hunter x Hunter manga is unfortunately not complete. The author has faced various issues that have led to intermittent breaks and an unresolved storyline.