Upa

Upas are a well merchandised character within the Steins;Gate universe, first seen as a dispenser prize, then later seen as a pillow. Upa is the mascot of the in-universe anime RaiNet Kakeru, which both Faris NyanNyan and Mayuri Shiina are big fans of. While Mayushii likes to collect Upa merchandise, Faris prefers playing the game Rai-Net Access Battlers based on the anime.

It turns out later on in the story of Steins;Gate that a metal Upa capsule toy (which is rare compared to ordinary plastic Upa capsule toys) is actually an integral part of causing World War III in the Beta Attractor Field. This is because the metal Upa Mayushii originally wins as a dispenser prize, she drops and is then picked up by Dr. Nakabachi at his press conference. The metal Upa ends up with the thesis on time travel Dr. Nakabachi steals from Kurisu Makise, and because it sets off metal detectors, he takes it in his carryon luggage when he defects to Russia, preventing the thesis from being destroyed by a fire in the luggage compartment.

If this metal Upa is replaced with a plastic Upa, Kurisu’s time travel thesis burns up in flames in the luggage compartment after Dr. Nakabachi steals it and flees to Russia, thus preventing World War III from happening, at least on the Russian side. Preventing the death of Kurisu is also necessary to prevent World War III, on the American side, given her involvement in research at Viktor Chondria University with some of the people responsible for the war. Preventing World War III in the Beta Attractor Field by having Dr. Nakabachi steal a plastic Upa instead of a metal one and saving Kurisu’s life is necessary to escape the Beta Attractor Field and achieve the Steins Gate world line.