The Citadel at the End of Time has streaks of gold throughout its architecture as if cracked or broken and then repaired, a famous Japanese process called "Kintsugi." It is considered a way of accepting flaws and marking one's appreciation of imperfections. This gives insight into the nature and manner of thinking of He Who Remains.
According to production designer Kasra Farahani, the Citadel at the End of Time was visually inspired by the Xanadu mansion in Citizen Kane (1941), the Petra City in Jordan and the Hearst Castle in California: "Basically, you have this grand fantasy space of a black asteroid inside of a nebula, and then you have these assorted grand architectural styles cherry-picked and collided together."
The Marvel logo featuring a voices from Marvel characters and two black holes was inspired by the sci-fi film Contact (1997), which featured a trip through black holes.
This episode marks Jonathan Majors physical debut in the MCU. Here, he's playing He Who Remains, a variant of Kang the Conqueror, the role he later played in Ant-Man and the Wasp: Quantumania (2023). Marvel had big plans for Majors until he was arrested for domestic abuse and was promptly dropped by the studio.