You know how in Dungeon Meshi you have:

Laios' party with the main story, the A-plot,

Kabru and the canaries have the B-plot,

And Shuro, Namari and their parties with the governor as the third plot line, the C-plot?

Imagine a 4th party with a storyline that doesn't impact the main story of Dungeon Meshi right until the end, and even then, it doesn't impact in a bigger scale either. But it contains artificery, dark magic and more chimeras and monster cooking.

That is the D-plot of Dungeon Meshi.

(My dumbass DM ocs)