The "Remi version" is the prequel game that you play as Serra's sister Remi 2 years before the events of the main game. The story helps explain how Remi became Lilith's top lieutenant and Dior's origin etc. The game is currently exclusive to Saefix's patreon.
Before getting sick Saefix ran into some writer's block for the main game and started the prequel game to help, his goal was (and still is) to finish the prequel then continue the main game. The prequel is almost finished (1 or 2 more updates and it will be done) but unfortunately Saefix fell ill and this has caused the major delay we've been experiencing. I am currently helping Saefix with the next update it will contain the next 2 levels/chapters and subsequent boss fights to go with them and many new improvements such as sound effects, door animations, and BGM!, these improvements are planned to be in the next main game update as well.
This game and Slugs and Bugs by Anaximanes are among the only good ones I know.
After we finish our comic project and helping Saefix, Saberdyne Systems are seriously considering making our own game along these lines (Different story but all the same kind of parasite and corruption/possession themes) Just keep an eye on us for now.