Finally a good ending!
@HaracasAye I'm thinking in my head canon that they arrived back in the past around 2 - 3 months (the earliest I could think of) before the disaster. That's plenty enough time to gather the allies (Jung-woo) and immediately destroy the damn doomer cultists. Have all the nations of the world unite into a singular government with public funding and knowledge all going in it, It would most likely take enough time to prevent it from happening as all the geniuses all over the world would gather and with unlimited funding and drive to save humanity from extinction, I honestly think it would only reach a few weeks before a plan to successfully prevent it and secure mankind is finalized.
Since they've built a freaking space station (assuming that it was only China who's doing all of it) and even managed to reach and construct on the surface of Mars. So its either going to be them correcting the ozone layer, send back Jupiter to its natural course and readjust earth and also prevent the moon from shattering-- OR build literal colony ships and move the entirety of mankind to another hospitable earth-like planet.
Dammit if they only kissed or at the very least hugged each other at the last panel and provided what they are about to do.. But anyways, thank you so much to the translator or translators for translating pretty much 2 seasons of this! And of course not to mention, the author and artist! thank you so much for creating a very unique manhwa. Honestly, I was about to drop this midway due to it being confusing (especially on season 4) and some other nitpickings but thank fully I didn't!