Edwin's cheat ability is simple.

Write in a diary, grow stronger.

Unfortunately, someone else keeps reading it.

After accidentally saving the future villainess's mother, Edwin is welcomed into the ducal household, where Serifina secretly discovers his diary and becomes convinced it contains mysterious prophecies of the future.

Meanwhile, Edwin continues filling its pages with brutally honest observations, completely unaware that every entry is quietly reshaping the fate of the girl destined to become the story's greatest villain.