She is the rich daughter of the General's Mansion.
He is the bodyguard and attendant of the General's Mansion.
She died in the disaster, awakening the potential source of her soul, and traveled to a place called the 21st century.
She couldn't let him go, and with the help of Pluto, she returned to the era when he existed, but he had become the king of a country, married the queen, and did not recognize her with a different identity.
They are so close, but there are thousands of years between them!