This King is immune to poison

Leonis summoned Shi Xiaobai and company to his chamber and engaged in a tirade that seemed like he was blaming Shi Xiaobai for secretly eating the holy tree's fruit, but in fact, the truth could easily be guessed. Leonis wanted Shi Xiaobai to head to the Infernal domain to kill the Infernal King.

Although it was unknown what benefits Leonis would gain if the Infernal King was killed, it was not something that mattered to Shi Xiaobai.

On the contrary, he was rather grateful to Leonis for giving him some idea what was the puzzling "King's Mandate" that the Absolute Choice had referred to.

Although ending the Age of Bravehearts and the King's Mandate both pointed to 'killing the Infernal King', resulting in a contradiction, heading to the Infernal domain to kill the Infernal King was still the best choice.