Why Jujutsu Kaisen's Yuji Has Such A Strong Resistance To Poison

When Yuji ingests the finger of Sukuna, The King of Curses, it bestows a host of super abilities. One of his most essential is poison resistance. The clearest example fans get of this is during the "Jujutsu Kaisen" Manga Chapter 61 (via Viz) or anime Episode 24 (via Crunchyroll). This is the climactic battle of Nobara Kugisakia and Yuji against Eso and Kechizu. The two heroes have to deal with Eso's Decay technique, which hits its target with a lethal poison. However, it's stated that while Yuji might feel the pain of poison, he is immune to it thanks to hosting Sukuna.

We also see Yuji's poison resistance come into play in Episode 12 during his battle with Junpei Yoshino as he deals with the poisonous attacks from his Moon Dregs. The Moon Dregs not only look like ghostly jellyfish, but they also have a horrible toxin that can burn their victims. However, even when the cursed creatures sting Yuji, the toxin has no effect on him. 

With Sukuna regarded as one of the most powerful curses in the series so far, it makes sense that having even a fragment of his power would grant such an immense resistance to poisons.