It's not a joke.
"With a twin in the picture, even if you were to be killed, your twin could always take your place and nobody would ever know," The man spoke with a smirk as he explained, "And there is also a possibility that the one who kills you might just be your power-hungry twin."
Hecathe's lips twitched as he heard this and he was clearly not amused to know this.
"That's some sort of a sick joke, isn't it?" Hecathe clicked his tongue as he questioned.
"But it's not a joke," The man stated as he tilted his head, "Why else do you think there was such a ridiculous rule?"
The three willows of spring were clearly power-hungry manipulators who didn't care for anyone but themselves. The only reason why they were in power was also because of a lot of blood-shed and conflict. With all this considered, it shouldn't have been hard to believe that they would go as far as to make such a rule, however, somehow Hecathe was still a bit shocked and disgusted.