The Ilenia Empire, a place currently known as the most peaceful and safe, overflowing with resources and supplies, where conversation and laughter never cease from the center to the outskirts. The wealthiest superpower in the world.

And there, the most talked-about figure, the empire's greatest genius mage and head of the Sylvester County.

Dekaian Sylvester

Welcomed by all citizens, gifted with a brilliant mind, overflowing wealth, power and prestige that even the King cannot ignore, and even a bewitching, insane beauty—he seems perfect.

But in truth, he has only one weakness.

...That is, his sister, Ariel.

After suddenly losing his parents in a mysterious carriage accident, Ariel is the only family Dekaian has left.

His sister, six years his junior, has been very, very severely sickly since birth. Collapsing, fainting, headaches, and insomnia are daily occurrences. Because of her long-unused muscles and fragile body, every time she wakes up after fainting, she has to practice walking step by step like a newborn again.

Dekaian could not afford to lose this one and only sister, who is both pitiful and lovely, so he pours all his focus into magic development and treatment for her recovery and stability.

Thanks to those years of obsessive effort, Ariel's health is improving, but to put it nicely, she still has a body like glass that seems ready to shatter at any moment, with no sign of true health to be found.

Then one day, Guest appears before him...