It was made in RenPy originally, it was ported to Unity around time of Ch21-22 release. Renders are made in Koikatsu. Prologue stuff was added along with Ch39 Part 2 release, new intro, new scene and voice acting for Chad. History isn’t saved currently because each rollback history entry is entire state which has to be saved, so saves would be 200 times larger if it was saved (so instead of ~15-150KB saves would be ~8MB each). This will be changed with engine upgrade, but that wouldn’t happen this year, it’s a massive project and improved save format is just one small part - but it will store state more efficiently so saves will be as small with history.