After a peculiar gacha draw, an unfortunate individual finds themselves reincarnated in a fantastical realm as the young Ein Roundheart. Gifted with the ability to neutralize toxins, he pales in comparison to his brother's impressive combat prowess. Despite his efforts, his father and stepmother favor his sibling as the heir. Events take a twist when Ein crosses paths with Krone, leading to his expulsion from the family. Seeking refuge in the girl's homeland, Ein is unexpectedly hailed as the crown prince. Thus begins a fresh chapter in Ein's life as he endeavors to prove his worthiness of the royal title.