pg.4, the extra stretchy loungewear set comes from a brand called "Mujiqlo", a portmanteau of two very popular brands in Japan: "Uniqlo" and "Muji". Uniqlo sells clothes, Muji sells mid-high quality homewares
pg.13, a "Batsu Game" is a game where the loser endures some sort of (usually small) punishment. Jdrama takes it up a notch by making them life-or-death situations like in Battle Royale, Liar Game, Kaiji, and the recent "Alice in Borderland"
pg.17, Miyamoto shows his vaccination marks from the BCG Vaccine, an immunization that Japan uses to inoculate against tuberculosis. Their version comes in a 3x3 grid, 9 needle format
Also on pg.17, Miyamoto makes a reference to
"Toyama no Kin-san", a popular fictional Shogun judge with a large sakura tattoo on his shoulder