Also known as: ルートボックス, 戦利品の箱
A gameplay mechanic involving obtaining a set randomized items either from defeating the enemy, or from in-game or real world currency.
The word "loot box" is first popularized from FPS hero shooter game Overwatch, where the randomized items is contained inside the titular box but is later used to refer to any similar model of microtransactions; similar to "crates" in Team Fortress 2.