d by dy

Away from where you sit and away from the complexities of human life was a village whose citizens consist of mathematical functions.

For example, commoners included the empathetic X. Lady Sine of X was known for her mood swings. Lord E-to-the-X was a loner that could only integrate with himself.

Citizens lived in predictable lives until the misfortunes of Lord E-to-the-X began with the arrival of an enigmatic traveler.

The traveler brought with him a mystical sword of immense power. A cursed sword. Indeed, the curse is such that it may be wielded by only the most worthy, the Dragon Warrior, the one who could survive the test of differentiation.

The villagers were not eager to be tested.

“I like being able to relate to people,” said X to Lady Sine of X.

“I’d rather be an emotionless Constant than join the family of those dreadful Cosines,” replied the Lady.

Only Lord E-to-the-X remained undaunted: “I am myself no matter how many times the differentiation.” He accepted the test, and vanished into a ring of smoke as soon as he touched the sword.

The sword’s name was d by dy.