noun
alternate reality game; ARG
A genre of interactive networked narrative that uses the real world as a platform, often involving transmedia storytelling.
あの代替現実ゲームは、参加者が実際の街中で手がかりを探す仕組みだった。
That alternate reality game had a system where participants searched for clues in the actual city.
Compound of 代替 (alternate, substitution) + 現実 (reality) + ゲーム (game), likely a calque of English 'alternate reality game'.