[Western Fantasy System] What a Massive Game

An ancient prophecy has been passed down since the Annals of Nursery Rhymes: [The Hero of the One Thousandth Generation will kill the Demon King of the Seventh Generation.] "What? Natasha is going to die?!" After hearing the prophecy, Renold Pandora, an innately frail, magicless Demon Prince, set out on a journey to study abroad with his twin sister, Natasha. What can he do, you ask? Talisman magic, spirit speech, fortune-telling, sorcery, Eastern medicine... Players: Help, this guy's System is different from ours! Uriel Knight, the foremost successor to the Hero of the Nine Hundred and Ninety-Ninth Generation, a young man considered Demon King-level at the Central Magic Academy, and Renold's eternal nightmare ever since he was fourteen. He's said to be determined to become the Hero of the One Thousandth Generation, kill the Demon King, and maintain world peace. Then, all of a sudden, on one accursed day, Renold and Uriel gained shared access privileges. From then on, the gates to a new world swung wide open before Renold. This world has been riddled with holes by players. To clean it up before it's too late, Renold is forced to embark on a journey where he's dragged along to fight monsters, level up, and complete quests. But, Father King above, can someone tell him why the System says every quest leads to a terrifying DIE ENDING? NO, NO, NO! That's not the ending he wants! [On How a Demon Prince Learns Magic] Hero of the Nine Hundred and Ninety-Ninth Generation: Today's first lesson is how to innovate with intermediate water magic... Renold: Sorry, Teacher, I only know talisman magic. Natasha: Sorry, Teacher, I only know talisman magic. Players: Hey, nobody said this game had an Eastern version! [On the War Between Natives and Players] Renold: I have wings and an innate ability to sense magic. Player: I have the whole map unlocked. Renold: Demons have a powerful natural ability to heal. Player: I have red and blue potions. Renold: Mess with Natasha and I'll beat you to death! Player: Wow, this NPC is so arrogant! Renold: You're the NPC! Your whole family are NPCs! ※ In a game riddled with holes by players who brought their Systems along when they transmigrated, the game characters fight back. ※ At first, the protagonist shares a body with his sister. As for who his CP is, that remains for the sharp-eyed readers to figure out. I prefer to let important story developments follow the plot. ※ This is a slow-burn, epic-style story, and all the worldbuilding is original.