。
This game is a work of fiction.
Literal
This game [topic-は] fiction is.
A one-line fiction disclaimer. Structurally the simplest possible Japanese sentence: [topic]は[noun]です. フィクション ('fiction') is a loanword from English, here used in the legal sense of 'a fictional work' rather than the narrow literary-genre sense. This kind of statement is part of the standard legal-protective opening frame found in novels, video games, and dramas, often combined with a separate character/place-name disclaimer.