The whole setting rotates around the Abyss both literally and figuratively: the city of Orthos is built around it, the city’s economy and society are focused on the explorers who plumb its depths for ancient and valuable Relics, and both of our main characters, Riko and Reg, are tied inextricably to its secrets.
The real star of the show may be the titular Abyss, a gaping, massive crater that goes down so deep, no one has ever plumbed its depths. Like, if every show in the entire anime season was hanging out in the Marianas Trench, Made In Abyss would be surfing the damn exosphere, merging with interplanetary space. Made in Abyss is the season’s clear winner by several miles.