Kaburato Castle is Sojo’s stronghold in the Vs. Sojo week. The fandom wiki and the chapter recaps use the castle name; this site used to say “compound.” Chihiro infiltrates to pull Char while the Anti-Cloud Gouger Special Forces meet Sojo at a bathhouse. Sojo comes home with a briefcase of semi-stabilized Datenseki the yakuza returned. He finds Chihiro in the courtyard. The last duel is here. Enten bisects Cloud Gouger. Sojo spends the ore. The house goes with him.
Castle, not myth
It is a crime boss’s house with a research hunger, not a wartime Sanso. Korogumi muscle and Madoka’s employment sit on the same street. Char’s regeneration is the stabilizer hunt that made the castle a lab. After Roar, residual Cloud Gouger charges wait for the Rakuzaichi. The castle does not. See Vs. Sojo, Sojo, Korogumi.