Transmigrated as a Hero, I Was Captured by the Adorable Demon King!

[Transmigration + Another World + Romance + No System + One Heroine] For some inexplicable reason, I transmigrated to another world. Everyone here is going crazy, insisting I'm the hero and demanding that I defeat the Demon King... Oh my gosh! Are you kidding me? I'm just an utterly ordinary college student! I failed to defeat the Demon King, but instead of executing me, she captured me and locked me up in her castle. As I continue exploring, I discover that some enormous secret seems to be hiding behind this world. But now that I think about it, this Demon King is kind of cute...