Agi Mawangnimeun Yongsa Appadeuri Neomu Gwichana

Reborn into a novel as the unawakened Demon King, Tatiana is imprisoned and exploited by demons who use her power for themselves. When her captors are killed by three heroes—Duke Siegfried Orleans, Archmage Kyrios, and High Priest Cesar—she nurses her saviors back to health, and they adopt her! Now, Tatiana is determined to awaken so she can be independent... But with three protective fathers watching her every move, can this 4-year-old keep her secret long enough to become the Demon King?

(Source: Tapas)