Indebted to the wrong people and facing death, former U.S. Cavalry veteran Booker DeWitt has one chance at redemption: rescue Elizabeth, a mysterious woman held captive since childhood in Columbia, a city that floats among the clouds.
I believe "free" is capitalized because the subject of this post is written in title case, as the title of a book or certain newspaper headlines would be. In title case nouns are capitalized; the word "on" is a preposition and thus left lowercase.
Whether a post's subject should be written in title case is a stylistic choice I have no strong opinion on.
English is my second language, not that it's an excuse, but I will never complain about it again! Thank you for correcting me, and for having the patience to respond to an, if I can say so myself, idiotic question!!
Ah yeah that explains it! Stuff like title capitalization generally doesn't have a lot of functional use unless you consume most of your media in English. Definitely not one of the things I'd focus on when learning English as a secondary language :>